One VERY IMPORTANT THING.
The MAIN reason why people miss their peak is stress.
First you need to understand the role of cortisol in the body. Cortisol is released under stressful (physical or psychological0 situations. It's main function is to make energy available if you need it.
When the stress is physical (training), that's fine because you do need the fuel. But when you are peaking for a contest, cortisol is your worst enemy.
Because it mobilizes energy. Basically cortisol will force the body to release stored energy. That energy is either stored in the muscle (as muscle glycogen), adipocytes (body fat) or liver (liver glycogen).
When you are trying to peak for a contest you want to store more glycogen in the muscles.
Bu cortisol pulls glycogen OUT of the muscles! The opposite of what you are trying to accomplish.
If cortisol is high because you are stressing too much, you will not be able to store the carbs you eat. So you will stay flat no matter what.\
Worse than that, carbs attracts water. So by eating carbs and not storing them in the muscles efficiently... and by mobilizing stored glycogen and pulling it out of the muscles you are attracting water outside of the muscles.... which makes the muscles look flat and make you look less defined.
That's why a lot of competitors get better at peaking as they get more experienced. Not because they use better methods, but because they are less and less stressed by the competition.
My best advice is to try to avoid getting stressed the day before the show. Don't look at yourself every 5minutes to see if you still got it... don't pinch the skin on your abs to see if you are still lean... do something fun...go to the movies for example.... try NOT to think about the contest. If you obsess over it the night before you WILL miss your peak. And take it easy the day of the show... that's why having a coach is important the day of the contest: he handles all the details so you don't have to worry about anything.
If you don't have a coach your biggest challenge, and the key to looking good, is being able to stay relaxed and stress free.