I was going to say "If you can't win with a dwarf army, give up now !" but I won't say that because some of you people might have only just started out :)
Anyway, the most important point to remember with a dwarf army is that you are slow, very slow. You are not built for a lightning fast onslaught. Bare that in mind ! Do not expect to be taking the battle to the enemy - they'll be coming to you, afterall they don't want to wait all day !
Dwarfs have such a strong defensive line that it's scary. Artillery, thunderers, quarrelers and gunpowder weapons. When the enemy does arrive he will still have to cope with the toughness of 4 and the fairly decent combat abilities of even the dwarf quarrellers.
On top of that an enemy may aswell forget magic, Dwarves are virtually impervious to it. Extra dispel dice and plenty of magic defence for combat units. Dwarf armies on the other hand are very good at their own brand of magic, notably the anvil of Doom which can pick enemies off from afar.
If you're playing the Dwarf army, all you really have to do for the first 2, 3 or 4 turns is decide who to shoot at next - it's quite good fun watching the enemy units wither away into ineffective combat units which your hammerers will dispatch in a single turn.
I guess what I should be writing is not, how to win a battle with a Dwarf army but more, how to make sure you are not beaten.
So, here are the mistakes to avoid...
- Keep your slayers away from enemy missile fire - NEVER march them towards missile troops without some cover (ie, behind another unit)
- Do not spread your units across the whole table, they will not be fast enough to provide support if things start to go wrong.
- Do not bother trying to outflank your enemy, it will not work.
- Do not become too predictable (this could be difficult for a dwarven general though !) Maybe try using some miners every now and then to screw up your opponents plans and hold back some of his advance (it really will annoy him/her !)
- Take some artillery and some missile troops but keep your army balanced. You will not be able to shoot your enemy to death before he reaches your lines so you will need some good quality combat units to receive his charge.
- Keep Slayers for those big beasties that might be coming, they have a great slayer ability so never need more than 4 to wound and also have slayer weapons so are quite flexible.
- Try to take out 1 unit at a time when firing missiles, if you rout a unit in combat, do not pursue if there are any other enemy nearby, you might regret it ! Keep you battle lines nice and clean and watch the enemy break against it like the sea against a cliff wall.
- If you can take some Dogs of War consider a cavalry unit. Keep it tucked behind your lines and move it to strengthen the part of your line suffering the greatest onslaught. This unit could also be useful for pursuing routing troops if the opporunity presents itself.
Last but, by no means least...
Make full use of runic items !!! They are awesome and can be combined to devastating effect. A Dwarf King should be next to invincible in combat against all but the greatest and most fearsome of enemies (think, something harder than a dragon because Dwarf Kings could easily eat a dragon for breakfast !)