Stay Hydrated!

Drinking water and keeping your body hydrated is very important. Not only is your body mostly comprised of water. Water helps food digestion and helps your body absorb vitamins, minerals, and nutrients that are helpful and healthful.
Many people have the belief that if they stop drinking water, that they will lose weight; that they ave "water weight". That is not the case. If you are not properly hydrated, your body turns into self preservation mode, and will begin to hoard water. As it does not know when the next time it will get some.
Therefore, when you work out, make sure that you are breaking a sweat. But most importantly, make sure that you drink plenty of water.
When I work out, I visit the water fountain in the gym in between sets.