I have intense intrusive thoughts. The only technique that works for me is to close my eyes and picture a slice of lemon in a cup of tea. I focus on the lemon in microscopic detail - the rind, the oils that come off it, the fruit in sections, etc., and on the tea - its color, its aroma.

I don't know why this works, but it does. I have to really focus to drive the intrusive thoughts away and that takes time. I spend a lot of my day fighting my brain.