NOTE: This is mainly directed to noobs.
For a good "push" (an attack on an enemy crown tower), you need 3 types of troops:
- DPS (Prince, P.E.K.K.A., etc.)
- AoE (Witch, Wizard, etc.)
- Tank (Giant, etc.)
Keep in mind the 3 different types of troop cards (DPS, AoE and Swarm) work in a scissors-paper-stone way:
DPS kills AoE
AoE kills Swarm
Swarm kills DPS
A tower is a single object. Therefore, a DPS troop is essential (either this or a swarm, but a swarm can easily be taken out by arrows). A DPS troop, like a Prince, is easily killed by a cheap swarm like a Skeleton Army, so use a Witch or a Wizard to support.
The problem now is that the AoE troop is usually quite squishy and will quickly killed by a tower. The DPS troop sometimes can take damage however is unreliable. For a truely unstoppable push, you would need a tank; a troop like a Giant with high hitpoints, especially one that only attacks buildings. You do not want your tank to be distracted.
If you can successfully play a good push like this, good luck! The tower is (usually) yours!