learn to pass guard and half guard using your size/weight as an advantage. Once you get side control, learn to keep them in side control, and begin attacks on the far arm(americana->kimura).
if they are attacking you, learn butterfly position and get double unders, or over under control. engage and destroy, or sweep and start your guard passing to get to side control.
side control to back is a good option. learn to take their back and not let them escape.
If you ever feel you are too big for a person to practice technique(too much strength), make your preworkout "something cardio", and gas yourself out.. so that when you're in class, all you have left is technique.