I've frequently had difficulty getting to sleep for the last few years - an unwelcome change, because I used to be able to sleep anywhere, on anything and in practically any conditions.

I've tried most of the remedies suggested in the thread, but the one success I've hit on is the most bizarre: I recite Bob Newhart sketches in my mind. I've no idea why this seems to work because the sketches are funny, and you'd have thought they would tend to liven the mind up rather than calm it down. I suspect they act as a kind of anchor for the mind to hang on to while it drifts off, and keeps me from being distracted by lots of other stuff.

Otherwise, good exercise in fresh air has to be the best remedy.