1.) Kick, kick, kick, kick. 
If you can’t keep your legs moving you’ll have an extremely hard time improving. so condition your legs during practice during kick sets. During regular sets focus on your kick because we tend to slow down our kick when we are in practice, make sure you keep kicking and have purpose for it.  
2.) All of your walls count. even during practice make them count because that practice will make your walls stronger during races. 
3.) If its a sprint like a 50 make sure to have minimal breathing. I only breathe twice during that race.
4.) Your start. Reaction time and distance is important. You have to be able to get off that block and you have to get off that block fast.