Three mantras for training and life:
1. "Get in the game" - Don't be a spectator for your matches or just passively enter into them. Be aggressive and try to control the rhythm, movement, and pacing of the match. Don't just be a "participant" - Be IN COMMAND.
2. "Keep moving" - Don't always maintain the same sparring stance and hand positions. Change the position of your body and hands, and stay fluid. By remaining still, your opponent can read your openings easier. You become predictable and give an aura of less confidence because of your rigidity. KEEP MOVING.
3. "Play your own game" - Don't care what your opponent is going to do or how skilled they are. Go with your own game plan and force them respond to it. Sparring (life) at its core is about willpower. If you cede your willpower to your opponent, you've already lost. EXERT YOUR WILL onto them - even when counterattacking!
Also, remember that no matter how good you are, sometimes you'll win and sometimes you won't. Losing teaches you more than winning. What matters most is how well you live up to your potential, not what the end "result" is.