I'm looking to get those 250 gems for reaching the crystal league without using too much elixir, any suggestions?
For me, I got to about 2300 trophies just by town hall sniping!
A nice, cheap, tactic is to max your army camps with archers or fill half your army camp with barbarians and the other half with archers. I'll give you 3 reasons why it's effective. 1. Archers and barbarians are super cheap troops and they train very quickly. 2. They're super good for getting Town Halls that are located outside of the base. 3. It's very easy for these troops to get 50% on even a very hard base by taking out the exterior buildings.
If you haven't noticed you also gain trophies for defending your town. Build up your defence a bit so you have a good chance in victory. Do the occasional attack once you gain all your troops but limit the amount of troops that you send to battle.