do what I do, don't keep track of score at all
so some opponents might cheat a few points off you once in a while by changing the score
big deal its only a game, not like its your career at stake
if you have no idea of the score you can just hit the ball.
Same thing goes for thinking about how you are hitting the ball, (ie do not think are my feet in position?, are my shoulders turned? etc etc), rather just think about what you want the ball to do, not how you are going to do it. Visualize where the ball is going to go and how its going to fly after you hit it.
My choice in choosing the ball path almost always means sending the ball to where my opponent is not, I think that is really the key to tennis, sending the ball to where opponent is not, that always creates problems for all types of opponents, and you really don't have to think about it, because its that obvious.
I'm 5.5 level. all the above works great for me. I play absolutely 100% identical at match point when im going to lose, match point when im going to win, in matches and in practice.