Duck Island is the best level for this. I used a fast plane with cluster bombs, the Frozen Fire. I flew in circles or figure 8s in the center of the map, trying to lure enemies into my fire and dodging as necessary. Grab any powerups you see, too.
If you lose a life during a wave, quickly press the Search button on your phone, wait a few seconds, and press the Back button. The game should say "Resuming" and then give you the option of continuing on the same wave with the number of lives you started with.