Body triangle with a guillotine style hold (not submission or you'll wear yourself out).
That is pretty generic advice as you haven't really stated if this is for MMA competition or self defense and if your goal is to advance your position or simply to tie up your opponent.
Robber guard is also nice for avoiding damage AND for advancing your position. Rubber guard is like a roundhouse kick. Easy to learn, lifetime to master. Find a good coach/instructor!