Try mini-tennis. It always helps me get my timing and technique back on track when I drift off. Focus on split steps, and slower and controlled swings but still your full forehand motion.
I know most people want to bash the ball from the first hit, but honestly if a person can't rally consistently in mini-tennis they'll never be consistent when playing with the full court. I'm not assuming you're like this, just that I've come across so many people over the years who are like this.