Move less.
If I had one piece of advice for the physical aspects of self-defense, it would be two words.  Move less.

Fighting is like marble sculpture.  It isn't like painting or architecture.  It is like sculpture.  Because moving well has nothing to do with adding things.  It is all about cutting things out.  You make a sculpture out of a slab of marble by taking out all the rock that isn't the form.  Sculpture is removal.

So is the art of good movement.  Absolute efficiency is not having a millimeter of unnecessary motion.  You don't defend if the strike is going to miss by a fraction of an inch.  Your own strikes do not go through any unnecessary distance.  Avoid decelerating to zero except with linear impact.

In sparring, there is a lot you can do with extraneous motion.  You can fake, disguise your telegraphs, change your rhythm.  But when you need to take someone out, for that matter, when you need to do anything quick, no extra motion.

And that's not how we teach it, usually.  The good martial artist can do more stuff than the beginner.  He can do the flashy moves.  The TV martial artists-- Bruce Lee hitting bad guys who just stand there in rapid fire strikes, clearly five times as fast as the bad guys can move.  Congratulations.  Those are the skills you need to beat someone 1/5th your speed-- and, in case you missed it, if you have superspeed you don't need any skill.  The best martial artists move more than the beginners.

And one of the side effects-- if the stakes go up, it becomes even more critical to move less.  A knife coming at your belly has no margin of error.  Bad things require maximum efficiency, not more cool moves.

The best fighters move less.  The best fighter, the best athlete in any speed game, moves less than the second best.  Not more.