One of my Android friends swears by constantly dumping/cleaning the cache of the DS app. She does it before and after every time she uses the app, and it has helped a lot with the crashing and lagging issues she was having. It's the cache of the DS app that needs dumped, not the cache of the whole device (although that certainly wouldn't hurt, either). From what I understand, DS accumulates a lot of junk during each play session which ties up your available RAM, which then leads to crashes and lag. This is my (technologically disinclined) synopsis of discussions I've read about preventing crashes and lag. Since I'm on iOS and don't have to do any cache dumping or RAM management, I have no idea the procedure for doing it on an Android device. Instructions are surely online somewhere, though.
I hope it can help! Lag sucks.