What's the best way to improve training?

An intentionally vague title for you. To improve the quality of your training, if you train in an external style such as TKD, MMA, Karate, is to work on your endurance. Stephan at GrappleArts.com says, "Endurance is the key. It doesn’t matter if you run in the park, skip rope, swim in a pool or go mountain biking: if you aren’t training to increase your stamina you are short-changing your potential on the mat." While his focus is obviously grappling, this applies just as much to the striking arts.

When I was doing full-contact, boxing smokers, and kickboxing, I'd run, spar, and occasionally sprint. I later used the best training equipment for a martial artist yet invented, IMHO, the VersaClimber, for rounds of three minutes, followed by 90, 60, or 30-second rest periods. I also would do burnout bursts of speed in the last thirty seconds of every round.

I agree with Stephan because more endurance means you can train longer, with better technique, thereby making more improvement that if you are exhausted and sloppy. If you have energy to burn at the end of a round, you can finish with a flourish to win the round, or, in a fight, fight all-out without letting up to rest (if your technique is good enough).

See Stephan's post for some ideas, plus check out his article, Cardio for the Martial Arts.