Choose a base which you think you can take on. Never try to chew off more than you can bite as it will most probably bite you back.
Try to take out the defenses that will harm your troops as early as possible. I.e. if you’re using archers and barbarians, take out the mortars and wizard towers first. If you’re using dragons, take out the air defenses.
Use your spells. If things aren’t going to plan, use your spells to aid your attack. Using lightning on enemy clan castle troops is always a good tactic.
Play to either at least destroy 50% of the enemy base or destroy the enemy townhall. This will guarantee you a win. If you’re feeling confident, take the whole base down.
Attacking for Resources (farming)
The art of farming is when you artificially maintain a low trophy count and attack bases for their resources and not their trophies.
Choose a base with low mortars, wizard towers and xbows. These defense units will make mince meat of your lowly farming troops.
Use an economical army. Use the smaller troops like barbarians, archers and goblins. In the end, you are just trying to take resources and not the trophies.
Aim your attack towards the resource storages and collectors.