One thing that can throw you off more than anything is playing at the wrong tempo. It's one of those bizarre things that others can notice but you may not realize until it has already cost you a couple games. While we tend to focus on telling players to slow down and play more deliberate, for certain players that might be the worst advice to receive.
We all have our natural tempo that just feels right. I know that I play my best with a slightly above average tempo. In my last match, I played scotch doubles against a player that played fast and another player that played slow. It didn't matter which was which, what mattered is if one played faster or slower than optimal for THEM.
Try experimenting with your tempo until you find that sweet spot. You might think that you play best fast or slow, when after some testing, you may be wrong. Once you find the perfect tempo for you, you'll play better than ever!
Hit 'em straight - and fast...