Once you "get in stroke," you can stay in stroke by hitting a few balls or a rack or two. Thus you see pro players take one practice rack before the match starts. No tournaments, okay, hit balls for 30-45 minutes just to stay in stroke and be ready. Worked pretty good for me.
Here's a short cut no one ever told you about before (except maybe me). I call it the Hard Hit drill. Set up long straight in shots from all different angles. Hit the ball pretty much as hard as you can, over and over. Don't worry if you're making the shot or not. After awhile you will start making some. Do this for 30 minutes (using both corner pockets) and then back off to regular speed. Voila, they're all going in! Try it, you'll like it.