One thing I found helpful was starting a piece a hair faster than the tempo I normally play it at. I know it sounds odd, but I found that when I tried to avoid playing fast, by starting a hair slower than usual, I would inevitably start speeding up to reach my normal tempo and then nerves would keep me accelerating past the right speed. Whereas, if I started already a bit faster than intended, I had no tendency to speed up further. It might not work for you, but it definitely helped in my case. This is from years ago when I was playing classical guitar, not piano, but I think the principal is the same.