They make these cool scales now that calculate your body fat %, your body fluid % along with accurate weight. I would suggest getting one of those. An average male should have about 60% fluid. An average female should have about 55% fluid. Weight yourself in the morning and evening. My son was a competitive fighter and used to weight before and after training. He would then calculate the difference to see if he needed to adjust his fluid intake. It's important to take your training clothes off before you weigh after training, because it holds fluids and will distort the numbers. Personally I think it's best to drink small portions through out the day, instead of one large quantity before class. However, morning training, as previously stated doesn't allow for that.
One other note, caffiene is a mild diuretic, and will make your body release more fluid. The effect is small and in most cases negligable. However, if you are having difficulty maintaining your body fluid level, you might want to avoid caffiene for a few hours before training. Otherwise caffiene can be beneficial in that it makes you more alert and gives you a slight energy boost.
As previously stated, clear urine means good hydration. Dark or yellow urine typically means you need to intake more fluid. If you are taking in large amounts of fluid and still have dark urine, go see your doctor.