One of the best is: DRINK YOUR WATER! People often confuse thirst for hunger. So instead of drinking water, they eat.
A good rule of thumb is to have at a minimum half an ounce of water per day per pound of body weight with the goal to build up to an ounce. Yes, you'll know where every bathroom is but you'll also be a lot healthier.
@cryptochain, really good point. So easy to confuse thirst with hunger. My mum used to always make me drink a pint of water when I was a kid before I was allowed to eat anything between meals.