Transitions and stand up attempts work much better after blocking a strike. Mind your stamina as it is seemingly the be all end all of determining factors.
So your mounted...
Step 1 : Block a Punch or three depending on your stamina, going for a trans or stand-up immediately will get you hurt
Step 2 : Be Wary of a Submission attempt
Step 3: Pick one of the five escape options (advanced transition left or Right into Half guard, Normal transition left or right to give up your back, stand-up attempt)
Step 4 : ?????
Step 5 : Profit!
Note if you give your back, you have no option to force stand-up. You can adv trans to half guard, or try your luck in Mount again.
Standing up is the easiest thing for the mounter to react to, then Adv Trans, then normal trans.