The very first thing I can do is point you to this guide right here:
Plasma's Ulitmate Guide to Kheldians
It's showing its age a little now but it is an excellent all round guide on Khelds and not only got me to grips with my Warshade but also helped me to fall in love with it. I recommend a read (might take you a while though!).
As for general tips, I would add a caveat to anything I or anyone else says as Khelds are getting a buff in i13 so our entire playstyle may end up changing. But for now, I'll attempt your questions.
Any generic tips would be good - Are there any particularly great or particularly rubbish powers?
Good: Dark Nova, Starless Step, Sunless Mire, Gravity Well, Gravitic Emanation, Unchain Essence, Dark Extraction, Shadow Cloak, Black Dwarf, Stygian Circle, Eclipse.
Not so good: Everything else. However, because Khelds are so versatile, people can have very different playstyles and what works for one may not work for someone else.
What kind of playstyle does the Human form have and what powers should I aim for?
Soft controls and buffs really. I only switch to human to rebuff myself or apply another knockback or stun.
How hard is it to slot and what should I focus on?
You will suffer for slots until around level 30, especially if you're going tri-form (which I recommend).
Can I tank TFs with the Dwarf reliably?
Without wanting to ignite the infamous debate, I say yes you can tank. Reliably? Less so. You lack a taunt aura and punchvoke only hits one target. If you can tank without those tools then yes, you can tank reliably.
Anything else I should definitely know in advance?
Persevere. It is hard at first and you may want to give up but once you get into your mid 20s, they really take off. Best of luck to you. 
@Dante EU - Union Roleplayer and Altisis Victim
The Militia: Union RP Supergroup - www.themilitia.org.uk
I am in exactly the same place as you, only maybe a month or so on - I have my WS and I'm at 25. I'd echo the previous post - plasma's guide has been a great help.
I've found slotting to be expensive and easy to get wrong. Forms come with four powers most of which need slotting on top of the powers you pick
I focused on putting slots into the form powers - Nova and Dwarf. My playstyle from 6 - 20 was largely that of blaster. From 20 - 25 it's been about the same, although you can now double mire, which when they both hit can make a massive difference to your DPS. I say massive, but these things are relative of course.
I have tanked when the main tanked faceplanted, and in a small team with experienced players. I haven't figured out how the taunt works, since you aim it at a target but I'm pretty sure it pulls more than one mob away (more experience players can sort me out here)
Anything else...? um, get macros to switch forms, you'll be doing it a lot if you want to get the most out of the AT
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I am in exactly the same place as you, only maybe a month or so on - I have my WS and I'm at 25. I'd echo the previous post - plasma's guide has been a great help.
I've found slotting to be expensive and easy to get wrong. Forms come with four powers most of which need slotting on top of the powers you pick
I focused on putting slots into the form powers - Nova and Dwarf. My playstyle from 6 - 20 was largely that of blaster. From 20 - 25 it's been about the same, although you can now double mire, which when they both hit can make a massive difference to your DPS. I say massive, but these things are relative of course.
I have tanked when the main tanked faceplanted, and in a small team with experienced players. I haven't figured out how the taunt works, since you aim it at a target but I'm pretty sure it pulls more than one mob away (more experience players can sort me out here)
Anything else...? um, get macros to switch forms, you'll be doing it a lot if you want to get the most out of the AT
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The Taunt is a targetted AOE affecting up to 5 targets as far as I know.
Slotting-wise I went with what made sense for each form. Human probably gets the least slots for me (I'm currently level 30). All I've really slotted are the hard control powers (Grav Well, Grav Emination and one extra slot in Inky Aspect), Hasten, Mire (1 Acc & 3 Recharge) & an extra slot in Stygian (1 End Red, 1 Recharge).
Dwarf I've slotted the Form itself, the Heal (1 Acc, 2 heal, 1 recharge at the mo), the Taunt (1 acc, 1 taunt, 1 recharge) and Mire (1 acc, 2 recharge currently).
Nova I've heavily slotted the AOEs (1 acc, 3 damage, 1 recharge) and slotted the 2 single targets a bit (1 acc, 2 damage).
I used the respec bug to achieve decent slotting in forms rather than spending them on the low level human powers, which I rarely use anyway.
Since the 20s I've tended to flit madly between forms. Generally start off with Human (with 5 toggles running, I've bound the V key to cycle them all on so its fairly easy) to Stun them all and get a mire going. Throw out a Hold on one (since its so heavy-hitting now as well). After that I'll either just switch to Nova for AOE death or Dwarf to mire again. I'll then either tank for a bit (if the team is low on tanks) or switch to Nova if I think I'll survive and we need the damage. Back to Human form to Stygian, either at the end of combat or mid-combat if I need it (at which point I'll also restun/rehold any survivors as well).
Its just a pity the Change into form animation is a bit long really. I'd love it to be halved to 1 sec.
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Its just a pity the Change into form animation is a bit long really. I'd love it to be halved to 1 sec.
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That would be awesome.
Following my late night post, I thought Id follow up with some random thoughts that Ive learnt from my Warshade.
Passives (aside from the Kheld inherent from i13) dont work in forms. So the Fitness pool is not necessarily a good investment. Stygian Circle at 22 makes Stamina pale in comparison and can take you from 0 to full in one hit.
A lot of Warshade powers are on long recharges so Hasten is a must. That gives you access to Superspeed which when coupled with Shadow Cloak = Invisibility. Add in your inherent teleport ability and you can ghost missions for teams and TFs easily.
Set bonuses from inventions do cross forms so theyre well worth investing in.
Buffs do cross forms so its common practice to drop into human form, fire off your buffs (Hasten, Sunless Mire etc) and then jump back into Nova or Dwarf to take advantage of them. To get maximum benefit, youll be swapping forms regularly so get some binds sorted out.
There is a secret to respecs as well when it comes to easing the slot crunch. Bear in mind that when doing a respec, you choose powers first, then slots so you can slot your forms before the level you gained them.
If youve ever played a defensive set, youll know what its like to go from uber monster slayer to punchbag in a matter of seconds. Khelds are like that a lot. Get used to it.
Warshades do mostly all negative energy damage. Stay away from Banished Pantheon, CoT and anything spooky.
Team as much as you can. Solo can be challenging even at high levels but on a team you can steamroller your way through a lot of opposition due to having more foes to drain from. Playing solo and playing on a team is almost a completely different game. Also on a team, you can adopt a certain role i.e. Blaster or Tank whereas solo youre having to play all the roles yourself.
@Dante EU - Union Roleplayer and Altisis Victim
The Militia: Union RP Supergroup - www.themilitia.org.uk
Hm, by the sounds of it human form is only good for buffing the other forms, then? :/ While I do want to experience the most of the AT that I can, I was kind of hoping it wouldn't necessarily mean I'd spend 90% of the time without being able to see my costume. I understand that Nova Form is great for pure damage, but would it be useful to fight in Human form in some situations for an extended amount of time, as well? And to invest into Human form powers in terms of slots and the like, as well?
Human's pretty much an "in between" state for a Triformer Warshade, mainly because Human form attacks tend to be low damage but high recharge (at least compared to the Peacebringer equivilants) and because Nova form, quite frankly, outdamages Human form on every front for a 'shade, especially with the two mires.
You *can* go heavy into Human form, but because of limited enhancement slots, you'll end up doing this at the expense of either Nova's damage or Dwarf's survivability. It's possible (albeit quite pricey) to outfit a Warshade so that Human form is very good at control/team support, Nova at Damage and Dwarf at Tanking.
Human only can be very effective and certaily will teach you about the inherrent and expect to use your nuke as part of your attack chain - with Stygian Circle the end crash isn't the problem you will find on blasters and with Eclipse you can handle the aggro of any mobs it misses.
I'd suggest looking at doing both a triform and a human only build when I13 comes out with dual builds
Mind of Gaia lvl 50 Defiant's first Mind/Storm 'troller.
Deadly Doc 50 Dark/Dark Corr
and lots more on Pinnacle,Union and Defiant
Well I have a level 50 triform ws and I cerainly don't use the human form as an 'in-between' state for the other two forms. Essentially I tend to use the 2 forms as useful adjuncts to the ws abilities. Need to lay down more damage against an AV? switch to nova form, preferably taking a sunless mire and eclipse buff first. Need mez resistance or need to draw aggro away from a teammate?..Dwarf form. Need to keep a 12 year old player's attention on the mission and off the costume your female ws is wearing? Either form will do 
Of course this represents how I like playing warshades and similar results may not occur if using your own playing style.
Having a warshade though has taught me loads about keybinding and macros. I can now not only switch between forms but I also have a 'panic button' bind that can drop out of a dwarf or nova and then activate nebulous form, just need the acivation time speeded up plz devs .
There's an awful lot of info out there on guides here and on the us forums...remember that a particular build may not suit your way of play.
best of luck with your kheldian.
Allodoxaphobia is the fear of opinions.
Everything we hear is an opinion, not a fact. Everything we see is a perspective, not the truth. MARCUS AURELIUS (121-180 AD)
So I'm slowly but surely pushing towards 50 on a hero - my first Hero above level 36, in fact, currently almost level 41 - and I inted to make a Warshade upon hitting 50.
Now, I intend to make a WS with all the AT-defining powers - all forms, fun things to do to corpses (Unchain Essence, Stygian Circle, the corpse explosion thing), the whole works. However, as I've never actually played a WS before, don't know the powers well and so on, I'd just like some advice from more experienced people.
Any generic tips would be good - Are there any particularly great or particularly rubbish powers? I know Sunless Mire and Eclipse are good, but that's about all I know.
What kind of playstyle does the Human form have and what powers should I aim for?
How hard is it to slot and what should I focus on?
Can I tank TFs with the Dwarf reliably?
Anything else I should definitely know in advance?
I suppose some generic build advice would be alright too, but I'd likely be overwhelmed if someone posts a detailed Mids' build for me or something. Keep it simple, I'm a noob to the Shades.