How do I stop this whole "my mind thinking" thing?

If I'm thinking what you are, you may do the same thing my mind does all the time. It's weird and I can't explain it, but all the time, stuff pops into my head and I think things over or I start thinking of all those parts I've tried to keep out of my mental mind's eye. I nearly always have stuff pop up in my head and it seems like no matter how I try to push it out, it's like my mind does the thinking even when I tell it not to. I hope I"m on the same page, but I have to say, it really, really maddens me.