Undead Tactics

General Tactics - You should fill out you army with large blocks of basic troops, as the will form your main line.These will be the anvil of your list. Move these units forward and use these to hold your enemy in place so you can line up cavalry charges and flank attacks. This is the hammer. One of the main cons of this list is if the enemies decide to sit back and shoot. Dwarves are especially problematic, as they have plenty of war machines and shooting, but will also beat your troops in prolonged fights. As such, it is critical to have a few units, either cavalry or werewolves, hunt war-machines to stop them weakening your line before you have a chance to strike back. Timing is critical, as attacking with your hammer before your anvil units can position themselves properly will leave them isolated and vulnerable. On the other hand, holding your hammer units back too long will mean that your anvil units will be destroyed, as they will likely not survive a prolonged engagement with enemy units.
Heroes/Monsters

• Revenant King - Fighting hero. Give him a cheap magic item, use his inspiring and Dark Surge to assist infantry units and charge enemies. Or mount him on a horse and use to support cavalry. Could take out units by himself.
• Vampire Lord - This guy is they hero you want. Expensive, but rightly so. Speed 7, 3+ melee, 6+ Defence, 8 attacks. He gets Crushing Strength (2), Dark Surge (3), Heal (3), Individual, Inspiring and Zap! (3). Absolute beast. Takes the best of a Necromancer and rams it together with a Revenant King, then buffs stats to stratosphere. Ten points to give him a Pegasus, which is a double edged sword, as you lose Individual and now have 5+ def but gain 2 attacks and puts speed to ten. A great all-round choice choice, but can you afford it?
• Liche King - Your expensive Mage hero. Not much use in combat, but with his dark surge, you can give Revenants up to a 26" move. You should mount him on a horse and have him Heal and Dark Surge your own units, and Zap! enemy units. Like all magic heroes, he should be used for support of units mostly, but a lucky Zap! may be able to break some units on its own.
• Necromancer - Your cheap Mage hero. Worse skills than a Liche King, but cheaper. Your call, what would the extra 70 points do if spent elsewhere?
• Cursed Pharaoh - Only take this guy if you are taking alot of mummies, as his Dark Surge and Inspiring only works on them. His main advantage is that he has the highest nerve for a hero in the entire list, and his durablity.
• Mhorgoth the Faceless - Holy Shiz, 400 points for this guy! Take the statline of a Pharaoh, give it 10 speed, then add every single rule (besides Individual) any other undead hero has, then add a breath attack and flight. He can easily turn a game in your favor. The down-side is his price. If he gets killed, in a 2000 point game, that's 1/5 of your points gone. Putting alot of your eggs in one basket with this dude. For the same points you take both a Vampire and a Necromancer. Morgoth and a troop of wights could hold an entire flank for a game.
• Undead standard bearer - Normal standard bearer. Has Inspiring. Not much else.

War-engines

• Balefire catapult - Our only war-engine. Generally a good buy. Like all war-machines, keep it at the back of the board. 

Cavalry

• Soul Reavers - Expensive cavalry. The best cavalry unit in the game, and the most expensive. Whether to take these verses Revenant Cavalry is a tricky question. Against lists that have little in the way of speed 8+ units that have Crushing Strength or Piercing shooting, like Goblins and Twilight Kin, their 6+ defense will allow them to run amok, killing low quality units with ease. However, if the enemy have these two quality, the cheaper cost of the revenants will often be a better bet.
• Revenant Cavalry - Cheap cavalry. Fast and efficient. Don't let them get pinned down or they will be killed. Crushing Strength 2 really helps them, and a regiment can often run about solo, unlike other cavalry that are support only. The models to these are absolutely beautiful, some of Mantic's best. Best for taking on small elite units, where Crushing Strength will help them, but will get drowned in attacks by hordes. Even though they can solo, they still work best as a support unit.

Infantry

• Skeletons - Your basic troops. They work well in large numbers. They are actually decent compared to other troops, as their inferior melee skill is offset by cost. The upgrade to spears is almost always recommended, as the points increase still makes them cheaper that other basic spear-equipped infantry, but increases their killing power quite significantly. They will not be able to last against most other units of equivalent size, and so should be supported by other units. The standard tactics should be to trap a unit with these while your revenants hit them in the back.
• Zombies - Even worse Armour than skeletons, but cheaper to reflect this. They will melt under determined bow fire, unless taken as a swarm or endless swarm. The sheer density of bodies and high nerve will make it a daunting prospect for most units, and is a god tier tar-pit for most. Protect their flanks, their nerve will be nothing if the enemy are tripling attacks. They have a large amount of attacks, so may be able to rout smaller units through weight of numbers. Like skeletons, do not use solo.
• Revenants - Poor old Revenants. They just do not know what they are doing. With the shields, their high defense looks good on paper, but they are too expensive to be used as meat-shields. They are supposed to be your elites, but they will melt against other armies elites. They could be used to support other infantry, but the extra speed and crushing strength of the Revenant cavalry makes them so much better for the points. Using them in hordes is the only real option, as they will beat out basic infantry hordes, and most elites that could challenge them cannot be taken in such numbers.
• Ghouls - Another iffy unit. They do not have Shambling, and are therefore your fastest basic infantry. If skeletons are zombies with better armor, then these guys are zombies with better attack. They suffer many of the the same problems zombies do, namely paper thin armor and the need to be taken in large numbers. However, they are even more expensive than skeletons, and cannot be taken in the quantity that zombies can. They have their uses, but are too expensive to be a truly competitive unit choice
• Skeleton archers - Not really necessary. The Undead are not a shooty army, and you should look towards the Balefire for ranged support, if any.
• Wraiths - I can see no real reason to take these guys. A troop is too small too take advantage of their defense, and the half-regiment and regiment are outdone by Soul Reavers. The 10 inch movement and fly is nice, but to enough to justify the price hike.
• Wights - Expensive, and only come in units of three, but Crushing Strength 4(!) really is brutal. These guys plus a Liche King on horse is a truly terrifying death star combo. The dark surge would help offset the Wights movement, and zap could soften up a unit for them. Not to mention heal. Adding a standard bearer on horse will make this unit ridiculously hard to kill, and very good at killing back.
• Mummies - Exellent arrow sponges, with defence 6+ and Regeneration, and with melee 4+ and Crushing Strength 2, good in a fight aswell. Combine with Liche King and standard bearer, and you have one of the toughest units in the game.
• Werewolves - First rate flank chargers.With Nimble and 9 inch movement, very easy to get into position for flank charging that block your zombies have tar-pitted. With those stats, they also make great war-machine hunters.