There are many techniques and tips that will make arrive at your contest in top shape. I have read many and tried some during my preparation for my last contest. Let's take a look at these tricks.
Sodium Load/Depletion
Sodium (Na) inside your cells has a water retention effect. So what you want to do is to "trick" your body into shuttling out excess sodium. To understand how this works, I'll quote Layne Norton who is majoring in biochemistry:
"Ok a little lesson in cellular biology to explain sodium loading. In the body sodium is present in large quantities compared to potassium and other ions. As a result the body's cells are always trying to pump sodium out and take postasium in. To do this task there are what is called sodium potassium pumps (I will refer to them as Na and K pumps to make it shorter in this reply) So what happens is Na (sodium) is constantly pumped out and K (potassium) is constantly pumped in. For every 3 molecules of K that come in 2 Na molecules are pumped out. Since this reaction is occurring against equilibrium ATP is used to power the reaction. Now what happens when you Na load? Well your sodium pumps have to work harder to pump out all the sodium that comes into the cell. Then when you cut out your Na intake the day before the show your body will continue to pump out Na at that fast rate. Since Na inside the cell makes you retain more water, all this water will be flushed out giving you the skin tight look. I believe sodium loading almost eliminates the need for water depletion."
Also adding potassium (K), it will help you stay hydrating as well as assist in pulling out sodium. When you are sodium loading, you will be holding more water than usual. Don't be afraid though, because if done correctly, this technique will get rid of the excess water you are holding.
When I did this, I was adding salt to my meals throughout the day. Three days before the contest, I stopped adding salt. Then the day of the contest, I ate foods that were very low in sodium.
Creatine Load
The idea here is to drop creatine (if you are taking it) about four to six weeks before your contest. Then 3-5 days before the comp do a quick loading phase. This is supposed to draw water into your muscles and away from under the skin. This will make you appear fuller.
I used this technique for my contest and did not have a problem with holding any extra water. I'm not sure exactly what effect doing this had though. So, you'll just have to try it and see how it works for you. I would suggest loading it 3 days before the comp instead of 5 though to be on the safe side.
Carb-Up
The point of carbing up before a contest is to replenish your muscles glycogen levels. This will make your muscles look full and hard. It is important to do it right though. For my competition, I carbed up the day of the contest only because I had a 7 PM show. I believe I needed to start the day before with about 200 carbs, then eat 300 carbs on the day of the contest like I did. It is very important to note that the amount of time needed to carb-up correctly varies from person to person. Some people need one day, some two, some three, and so on. You also do not want to consume too many carbs because you will appear flat and smooth. In order to know how much carbs to consume, you have to know your body.
