The Dark Eldar are an army of speed and maneuver. They are very fast, with high mobility due to their own inherent abilities and the availability of Raider Squads, Reavers, and the Ravager.
They must be used with care, taking advantage of these strengths while always remembering that like all Eldar they have low Toughness and light armour with saves that aren't as good as many of their enemies'.
You will have to out think your enemy and choose where you strike carefully. You should never get into a shooting duel with your opponenet, as you will either be up against troops with higher Toughness and better armour like the Space Marines and Chaos Space Marines, better Toughness and numerous troops such as the Orks, or great numbers and heavy guns like the IG.
Right here I'm going to say it: In many scenarios you do not have to kill enemy troops to win. You don't have to go head on across the battlefield at your enemy, instead you should concentrate on one area of their troops and pick them off one squad/vehicle at a time, using every bit of terrain you can to cover your advance. When you do strike, destroy the part of the opponent's army you have chosen to strike and then move on to the next, if it is favorable for your army to do so. If not, move back to cover; do not get bogged down in a static fight. Don't let your enemy get control of the battle, always fight on your terms.
AGAINST CRAFTWORLD ELDAR
I have found the Craftworld Eldar to be a very tough army to defeat. Dark Eldar and Craftworld Eldar have many of the same strengths and weaknesses. They are both fast, they can both put out a lot of fire, they both have high mobility, but they both have the same weakness in many of their troops.
The Cracftworld Eldar Aspect Warriors can present problems for you as they have better armour than most of your troops, and the close combat Aspect Warriors will strike down your troops in hand to hand if given the chance. Wraithguard and Wraithlords have high Toughness and are well armed with 3+ saves. They have well armoured vehicles such as the Falcon and Wave Serpent to transport their troops. The down side of this for the Craftworld Eldar is that these troops cost more than yours, giving you the advantage of outnumbering them. Your vehicles also cost much less than those of the Craftworld Eldar.
Against Craftworld Eldar you must assess the moves of your enemy and you must maneuver to take advantage of your superior numbers. You should keep a reserve made up of one of the following: a Wych squad in a Raider, a Scourge squad, a Hellion squad, and/or Reavers. This reserve force can make a decisive effect on the battle, either offensively to crush enemy troops, or to aid your own troops in escaping destruction.
Fighting other Eldar, you need a well balanced force, including a good mix of Warrior Squads, close combat troops, and heavy firepower. You will want splinter cannons and shredders for killing Guardians and the lighter armoured Aspect Warriors, but you will also need blasters and dark lances for killing vehicles, Wraithlords, Wraithguard, and the heavier armour Aspect Warriors.
No matter what you do in any Eldar vs. Eldar battle, it will tend to be a bloody affair.
AGAINST SPACE MARINES
You should outnumber Space Marines and you should take advantage of this. Attack one section of the Space Marine army with all you have, hit is fast and hit it hard. Don't let the Space Marine commander cut your troops down with ranged fire, close and close fast. Use your speed to catch him in a crossfire, don't give him time to think and plan.
Use Incubi back up by Raider Squads as strike forces, use lesser troops to draw fire away from your attack squads. Make sure you have some dark lances to take out the tougher foes and vehicles. Disintegrators are very useful against Space Marines so include some in your force.
AGAINST CHAOS SPACE MARINES
You fight these much as you do Imperial Space Marines. But you will need to take into account the availability of Daemons. Always be wary of the Greater Daemon's ability to possess characters.
AGAINST IMPERIAL GUARD
Try to strike at a flank or an isolated area of the Imperial Guard force, don't allow him to concentrate his fire against you. Beware of barrage weapons. Hit and run, maximize your Victory Points (VPs) while minimizing his. Remember that in many of the scenarios you don't actually have to kill the enemy, you can win by fulfilling the mission objectives.
You will need your fast troops, you will need splinter cannons for killing troops, and you will need dark lances for destroying the Imperial Guard's tanks. Use Wyches, Reavers, and Warp Beasts to attack vulnerable Guardsmen squads, but don't let them get caught in concentrated firepower from the Imperial Guard during sweeping advances.
AGAINST TYRANIDS
Move, move, and move when fighting the "Bugs," use blasters, disintegrators and dark lances to take out the big bugs like Canifexes, Zoanthropes, Lictors, etc. Use splinte rcannons and shredders in large numbers to take out the hordes of Termagants, Genestealers, Hormagaunts, etc. Most bugs have poor armour saves so take advantage of it. Even a splinter rifle will take most of these out! Just make sure that the Genstealers, etc. don't get to charge you.
All of your Raider Squads should be armed with splinter cannons. Use Reavers and Scourges with splinter cannons, disintegrators on your Raiders, and give shredders and blasters to your squads.
Keep moving and maneuvering, don't let the bugs assault your squads.
AGAINST ORKS
Maneuver, maneuver, maneuver. Take out isolated mobs with firepower, avoid most close combats as you will be faced with large numbers of Touhgness 4 troops who love hand to hand fightring. With the Dark Eldar speed you should be able to avoid close combat and stay out of the line of fire of most of the Ork mobs. Splinter cannons, shredders, and blasters are my favorite weapons against Orks. Move and fire, and use terrain to limit the Orks' ability to fire at you.
DARK ELDAR TROOPS' STRENGTHS AND WEAKNESSES
| Archon | Strengths: Good close combat ability and high Leadership |
| Weaknessess: Low Toughness | |
| Dracon | Strengths: Same as Archon, plus low points value |
| Weaknessess: Low Toughness | |
| Heamonculus | Strengths: Good at close combat, and the ability to use special weapons |
| Weaknessess: Low Toughness | |
| Incubi | Strengths: Very good in close combat, and good armour save |
| Weaknessess: Low Toughness, high points cost, no Fleet of Foot | |
| Grotesques | Strengths: Good at close combat, Feel No Pain, terrifying |
| Weaknessess: Stupid, no Fleet of Foot, need leader | |
| Mandrakes | Strengths: Shadow-skinned, Hidden Deployment, good at close combat |
| Weaknessess: Low Toughness | |
| Wyches | Strengths: Very good at close combat, Combat Drugs, and Wych weapons |
| Weaknessess: Low Toughness, poor armour save, no ranged weapons | |
| Warp Beasts | Strengths: Awesome 12" charge |
| Weaknessess: Low Toughness, poor armour save, no ranged weapons, only 3-5 in a unit, will attack nearest unit (friend or foe) is Beastmaster is killed | |
| Warrior Squad | Strengths: Good heavy weapons, reasonable cost, good Leadership, large numbers |
| Weaknessess: Low Toughness, no close combat weapons, poor armour save | |
| Raider Squad | Strengths: Fast, has a Raider transport |
| Weaknessess: Low Toughness, the Raider has weak armour and is Open Topped | |
| Reavers | Strengths: Good at close combat, very fast, good save, good Toughness, Combat Drugs |
| Weaknessess: High points cost | |
| Hellions | Strengths: Fast, hellglaives, Combat Drugs |
| Weaknessess: Low Toughness | |
| Scourges | Strengths: Deek Strike, Scourge Wings, good heavy weapons |
| Weaknessess: High points cost, no close combat weapons | |
| Ravager | Strengths: Fast Skimmer, well armed with three heavy weapons |
| Weaknessess: Low armour value, Open Topped | |
| Talos | Strengths: High firepower, multiple hand to hand attacks |
| Weaknessess: Unpredictable, they attract heavy weapons fire like a magnet attracts iron shavings |
Sample Army Lists
1000 Points Dark Eldar
1500 Points Dark Eldar
2000 Points Dark Eldar
(made with Army Builder)