I just wanted to lay out a few pointers i have picked up from battling dwarfs. My best friend plays them and we tango quite often.
1. Have plenty of war machines. Cannons and Rocket Batteries seem to be the most effective. If you can out siege the dwarfs, they will have to come to you, giving you plenty of time to shoot em down.
2. Run a 3x3 detachments and 5 handgunners with any combat blocks. The flank charge with a parent unit of 25 is usually enough to take out dwarf warriors, and sometimes even the nastier elite units. I have had the most luck with swordsman. The 5 handgunners will help chop down the units a bit ensuring you outnumber them.
3. The dwarfs get free dispel dice. Running an army with no wizards in it negates the dispel perk the dwarfs get. If the dwarf player takes runesmiths or the anvil of doom you will make him waste even more points by not taking any magic. When I run wizards against dwarfs they almost never make back there point costs. Even when spells do get through those guys are tough. If you do decide to run wizards, though, lore of metal is the way to go.
4. Watch out for the scout units (rangers and miners). An effective solution to this problem is to have 1 or 2 units of outriders sitting by your warmachines or wherever you think the scouts will go. With 360 degree line of sight the outriders will mow them down as soon as they pop up. One of the largest problems with outriders is their weakness against magic. With the dwarfs you dont have to worry about this little weakness. Outriders are an excellent choice.
5. Point your cannons at the warmachines/gyrocopter/anvil of doom, rocket batteries/mortars at the big blocks, and your shooters at the thunderers. It is important to take out all of the dwarf ranged units as quickly as possible. If you can out shoot them and make them come to you, you have plenty of time to worry about the combat blocks because the dwarfs are so slow.
6. 1 or 2 units of 5 knights can come in very handy for warmachine hunting, march blocking, flank charging, and stopping miners/rangers
7. Steam Tanks may not be a good choice against these guys. Cannons are the bane of stanks. Dwarfs can also cover their cannons in runes making them even more deadly. Every time ive run a stank against the dwarfs it has not seen combat.
8. I've never tried it, but a unit of huntsmen may be useful to take out those pesky dwarf war machines.
9. Try to take out any units that have dwarf heroes before they get to you. Humans do not fare well in challenges with dwarf heroes.
10. Hochland long rifles will usually not make back their point costs. The dwarfs are just too tough, and too well armored.
11. Usually engineers are looked down upon, but ive found them quite useful against the dwarfs. Putting them with cannons helps ensure you take out the dwarf war machines quickly. Pigeon bombs can also be useful for taking out war machine crews.
That is all i can think of for now, i will add more as i continue battling the dwarfs and learning new techniques!