If you want to win, you need to have at least 3 speeds- fast, faster and fastest. These 3 speeds require 3 different training methods.
Your pace during the race may vary. There will be times when you want to go all-out and other times when you are mainly coasting.
First, the fast speed should be the speed that you normally race at and the speed you do full lengths at. This isn't an all-out speed, but just under that. By training fast, you will be used to going fast and will naturally be fast on race day without any special effort or changes. Don't do much training at speeds slower than this (except recovery training) because your muscles will get used to this slower pace and it will become your race speed also.
The faster speed is what you do over 30 second courses. This should be a large part of your training because when doing 30 second courses, you will get used to going slightly faster than race pace, so your body will get used to going slightly faster and your times will get better. At the same time, 30 second courses develop the aerobic and anaerobic systems.
And you can practice moves and figure out what is the fastest way to do different moves because you get instant feedback in the form of counting time and penalties. With full length courses, it is sometimes difficult to figure our where you gained and lost time in practice, unless split times are done on different sections. With 30 second courses, you normally know where you gained or lost time, so you learn something with every run about what is the fastest way to do moves.
Third- fastest. Everyone should also do some speed work at times from 5-15 seconds. These are all-out efforts and develop the speed you need to be really fast. You only need to do these once or twice per week, but they should be a part of your training year-round. This is the way to get fast, in case you were wondering. The 30s and full lengths will help you maintain the fast pace, but if you don't have the speed to start with from doing very short courses, the speed you maintain will be a slow speed.
Don't get stuck in the same slow rhythm in your training. Slow paddling trains your muscles to go slow.
Vary your speeds, going from fast to faster to fastest. Avoid the monotonous slow paddling rut. The only exception is for short, slow recovery paddling, which isn't really training, but just recovery from training. Other than that, your training should consist mainly of fast pace (race pace, race length training), faster pace (30 second courses), and fastest pace (all-out efforts lasting less than 15 seconds long).