Well, let's begin with that. You have to use the cheapest troops: goblins, archers, and barbs because troops cost elixir too. When you are raiding, look for the same town hall that you have or a bigger but rushed town hall. Remember, you have to attack bases with full collectors, which are usually outside.
Next, RAID IT. Deploy the goblins first, next to the collectors. When they have taken all the collectors out, deploy the archers and barbs to get the town hall or 50%.