I've played CQC regularly since it released and am currently a level 49.
I've become much better than I once was, due to lots of practice, though I'm sure I still have much to learn. Here are the things that made me better:
Play to maximize your number of kills. Focus 100% on finding your next target ASAP and destroying it, then moving on to the next. Any time spent hiding from harm is potential points lost. You win by scoring kills, not by avoiding death. Prefer weakened targets over fully shielded or stealth targets, when you have a choice. Sidewinders and silent runners take the longest to kill and are best avoided when easier targets are available.
Get in the habit of using reverse thrusters to maintain distance when tailing an opponent in order to maintain your target lock for longer.This helps A LOT and many pilots don't know how to evade it.
Get the weapon enhancement whenever you see it, both to boost your kill capacity, and to prevent others from getting it. For me getting the weapon enhancement often quickly boosts my score by two or three, which is huge considering that a deathmatch is won in 8 kills. The weapon enhancement can be the deciding factor in who wins the match.
As soon as you are under fire, release chaff, look for shelter to break the target lock, and redistribute power to either engines or shields depending on which will help you more in that situation. If someone is tailing you closely, sometimes you can fly in reverse, and they will shoot past you, making them vulnerable to counter-attack.
Don't dogfight an opponent head on unless you are significantly better shielded than your opponent. Instead, use vertical thrusters to fly an arc around them, while shooting them at the same time. I find that this confuses many pilots and allows me to destroy them without taking much damage myself.
Learn to turn with flight assist off. For a very fast turn, disable flight assist and engage reverse thrusters. Then once you've whipped around, re-enable flight assist and redirect thrusters to forward. Boosting during the process can also enhance the speed of the turn. I routinely win "turning battles" using this trick.
Pay attention to who is winning the most. The best pilot can often be the most difficult to kill, and your time might be better spent picking easier targets. I've won many matches where I beat the "best pilot" by just avoiding him and focusing on scoring through hitting easier targets. But if you see the best pilot in a weakened state, this is the time to strike, because destroying him costs him respawn time, which gives him less time to score more kills against you.
When facing probable death scenarios, such as 2 ships shooting you when your shields are down, you have no chaff, and no place to hide, try to take someone else out before you die, by concentrated fire or kamikaze ramming. Sometimes this can score you an extra point.
Kill steal whenever possible.
Accept that there is an element of luck involved in winning. Sometimes I win not because of exceptional skill but because 3 unshielded ships flew right into my lap at just the right time.