In order to not think about something you have to acknowkedge it's there, and continue doing whatever it is you need to do.

It's part of Acceptance and Commitment Therapy (ACT).

Distractions can work for awhile.

Or you can you can go extreme and do ECT or get a brain injury that effects your hypothalamus(?), or other things you really shouldn't do.

Otherwise, the more you tell yourself to stop thinking about something, the more you will.

I went out and bought myself a little elephant bracelet, so that when I want to stop thinking about something, I remember i have to acknowledge it.