Mouseman asks,

"what should a fast bowler be thinking about before, during and after bowling the ball?"

There is a lot to think about, and no one answer to that question. However, there is a simple process you can follow to keep your mind clear of useless clutter than distracts you from bowling well.

It was told to me a while back by ace coach Stuart Barnes:

1. Clear your mind. Once the ball is dead, relax and think about anything but what just happened.
2. Review. As you get to the stumps on your walk back to your mark, think about what happened and if it went to plan or not.
3. Decide. About halfway back to your mark, based on your review, decide what ball you will try to bowl next.

Then when you run in, all you think about is the ball you are going to bowl based on your calm, rational decision made during your walk back.

After you deliver the ball, make sure you get your fielding right, whether it's catches or just getting back to the stumps for a run out. Only one the ball is dead should you go back to the process above.

You might identify other thoughts creeping in that are more emotional. Try to keep these out by refocusing on the three steps above. It's not always easy, it takes work but if you can you will have a much more rational approach to bowling.