Usually play Three Musketeers on your side, split behind your towers (one in one lane, two in the other). Add Ice Golem or Battle Ram in front to turn them into an attack. Because they're so expensive, pairing them with Elixir Collector to build an elixir lead is a common strategy.
Tips
Don't put all three in one spot when your opponent has Fireball, Lightning or Rocket.
A split push with Battle Ram pulls your opponent in two directions.
Play them after gaining an elixir lead instead of at the very start.
Strengths
Huge total damage; hit air and ground.
Split across lanes, they put your opponent in a tough spot.
Weaknesses
Very expensive; spells can cost you a lot of elixir.