Get the right reasons behind what you're doing then keep repeating it until until it comes so natural to you that you don't need to think about how to do it. Even when you're not in the gym training you can reinforce what you already know by visualizing all the pieces that make up a particular movement. This will help you for the moment where you need to do it right off the bat. For example you said your left-hook needs some work to get right while you're in the ring, break it down by learning the different parts that make up the movement, then slowly start putting it together so that it starts to feel right. Don't worry about the power and speed that'll come later. Now you can isolate that punch and throw it over and over so that you'll be able to throw it with consistency everytime. Next comes the brains behind the move, start working on getting yourself in position to be able to land the left hook as if you up fighting a real opponent. Find the angles, what are the conditions that have to take place for you. For instance are you going to throw this as a counter to your opponent's punch? Just keep it basic right now before you jump into deeper thoughts.

By the way, we have a free ebook topic that you can check out if you would like to find out the different responses for the each punch. There's a good book there written by a boxing coach named Edwin L. Haislett that goes over the most of the techniques that's out there. It's a good reference in my oppinion.