Here are some bits and pieces to bear in mind if you take them along for the fight.
Charging
Don't deploy them opposite enemy cavalry units because you need to try and make sure you're the one who gets to charge. They get +1 on their strength if they charge (for the 1st round only)
Missile fire
Keep your wardancers tucked away out of sight in the early rounds. They only get a 6 ward save, thanks to their talismanic tattoos, which is not going to protect them much (also -1 to hit due to their skirmish ability)
Psychology
Try to make sure your wardancers are taking on the enemies fear or terror inducing units. They are immune to such wimpy emotions.
Skirmish
Don't forget that your wardancers can move very freely. No need for all the silly wheeling etc. They quicky cover ground and are good support troops for your rank & file or even dryads who have a 5+ ward save and higher toughness to soak up missile fire (note: dryads are skirmishers too)
Shadow Dances of Loec
- Whirling Death
Confers the killing blow rule - Storm of blades
+1 attack - Shadows Coil
4+ ward save - Woven Mist
lose 1 attack, always strikes 1st
How to Shadow Dance
Consider your enemy's weaknesses. What's happening around your wardancers ? Do you need to hold up the foe or cut through them ?
My Rules of Thumb
Does the enemy unit have a lower Ws ? Then use Storm of Blades for extra hits (providing the enemy toughness is not too high)
note: always use storm of blades if you're charging (+1 str). Unless you just want to hold the enemy up until reinforcements arrive.
Does the enemy have higher toughness ? Use Whirling Death those rolls of 6 will mean killing blows (no saves). It might be your only chance.
Are you receiving a charge or does your enemy have a higher strength and you're expecting to take hits ? Use Shadows Coil, also use this if you just need your wardancers to stay alive while your army comes to the rescue.
Are you facing a High elf army or special characters who will always strike first ?then use Woven Mist (probably the least useful)
note: Compare your initiatives first though. If it's the same you will still have to roll to see who goes first unless you won the last combat.
Finally
Important, note: You can not use the same dance on consecutive turns so have a plan in place for which dances you will use and in what order against enemy units if things are going well or badly.
I hope you found this useful. Happy wardancing.