This depends on your level. You are only looking for subs on a basic level, which is fine and effective, because even most pros don't bother doing really challenging, risky stuff in the ring (because it's too easy to make a mistake and get decimated)
Originally Posted by JawShattera
About the only sub you can go for under a mount is a kneebar or ankle lock. the best thing to do is just get out and fight for a better position in my opinion going for crazy leg locks from the bottom in that position is risky.
From the position there is also a RNC, but that takes a little while.
If you can lock down one arm and get the up there is a nice arm drag that, with the right torso rotation, can be turned into either an armbar, a keylock and a kimura. However, the up is really the most challenging part.