I am volunteering my thoughts in the hopes of getting more ideas. Critiquing me is totally welcome.
I go for a 3foul when:
-it's a very weak player and I really really want to win
-the person has demonstrated several times that they can't kick in this match on this table, for whatever reason
-the opportunity is there from the layout and he's already on 1.
The last one is particularly good against a superior opponent because it's an insult.
other thoughts:
--In forcing foul # 2, plan for foul #3-- Don't pop the ob out into the middle of the table all by itself. Go for simple and small, if you can. Baby shots can make tighter safeties and better opportunites for later.
--When you have fouled once and it's clear the opponent is looking to force foul #2, watch closely. Sometimes the way he hit the ob in order to hide it can help you figure out how to hit it: what spin, speed, point on the rail did the ob need to get to where it is now, and can you use that with the cb now to hit the ob AND a rail? Even if this ultimately doesn't help your next shot, it makes you feel a whole lot more in control and keeps your brain on offense.
--if the 2nd safety is truly lock tight and you have no way in hell to hit it, you still have an opportunity to harm his 3rd safety with your 2nd foul shot. Can you break up the balls to give him less hiding spots? If there are only a couple or few balls left on the table, can you freeze those up and prevent an easy bih runout?