Raid enemies that will give you the rewards you want, whether that is more elixir or just a better ranking. Plan your attacks accordingly. Pay attention to a settlement's Town Hall level, since you gain less if you attack a settlement with a lower level. Keep track of which troops can damage which aspect of a settlement you are raiding. Your goal is to send in units that can quickly destroy any walls, such as giants, and then clean up an area with smaller units and perhaps another wave of giants near the end. Remember also that your goal is to find as many spoils of war as possible without losing too many units in the process.