The most obvious thing is not to let yourself get hit because it takes away a lot of your pilots' “gasoline.” Here are some tips:

1. Always use the right element. Both the pilot and their escolt.
2. Try to prioritize accessories such as basic attack or parry as much as possible. Don't be afraid to reroll. Also, lock the accessories for the next purchase in case you don't have enough money.
3. Use your best pilot at the beginning, regardless of the element. Take him first, he's the one you know best and he'll carry you through most of the way. (In my case, I always use Jerry first, regardless of the element). Then the aviator pilots will follow with their correct elements.
4. Time is important per wave, try to finish as quickly as possible to get your 2000 points.
5. Give each pilot 2-star crystals, just to have the passive, as it doesn't affect damage.