tips for beginners:
upgrade archers, skeletons, max unkeep, mana and regeneration first
upgrade meteor and resurrect if you want do the job quickly
Summon a lot of skeletons (archers first) and when you had a hudge army, put auto On.
Bomb the buildings, your army does the dirty job.
Take an eye in you unkeep and summon some archers if it downs.
Frezze is useless.
orcs, zombies, etc... aren't so efective as they appears. Trust me: skeletons.
fun fact: a lvl 10 archer skeleton is better than a lvl 10 zombie, and cheaper.
Resurect after a bomb can help you to summon skeletons faster.
Diablo and Jeezebel are the best ones, but they are locked. So you, newbie, trust me: SKELETONS