Dark Elves are a fantasy "Special Operatives" force. They have staggering amounts of troops with unique abilities, and perhaps the best mixture of fast assault, skirmish, and mis- sile forces. On the down side, they are Elves, which means that they are expensive. My solution is to form the backbone of my army from infantry with very strong support of cavalry and special troops. This gives me enough numbers to survive any war machine/missile hits. Having said this, Dark Elves are not Skaven. They can not survive a prolonged war of attrition. Thus I also have Repeater Bolt Throwers, Scouts and Dark Riders to deal with any long range attacks.
This is perhaps the most important thing when playing with the Dark Elves: you must find the right balance: you have the troops for every situation, but they cost so much that you can not afford to miscalculate what troops you need and how many of them are required. Learning this trick is hard, but once mastered, this army is a positive joy to play with.
One way of building the units is "a Shackle". The idea is to support Some big, important unit with a smaller one that serves as a flank guardian/missile screen/missile support. Here are few examples: Cold One Knights and Dark Riders. Against armies with heavy missile support with high armor save modifiers, infantry shielded by the Black Ark Corsairs is an option worth considering. Witch Elves and Harpies. Harpies will act as a moving missile screen with their tough- ness 4 and 2 wounds.