The amount of water you should drink each day varies based upon who you listen to. The old standard is 8 cups of 8 ounces of water a day (64 ounces). From what I've heard that 'standard' isn't rooted in science, but it is easy to remember so it seems to have become the norm. I think most people suggest around 100 ounces a day for men. A big indicator to determine if you are getting enough water is the color of your urine. If it is darker than straw (pale yellow), you likely could use more water intake. Of course if you take vitamin supplements I think the urine color test won't be effective for at least part of the day.
You should also consider that drinking certain things: Coffee, alcohol, etc... actually cause you to pee out more fluid than you drank in. So, they increase the likelihood that you'll end up dehydrated. Do a google search for diuretic for a list of things to avoid if you are worried about becoming dehydrated.
The easiest thing for me to do in order to make sure that I drink enough water was to buy a good water bottle. Once I got a good one, I carried it around with me everywhere and drank from it often. Of course, I lost a few of them in the beginning (put it down and forgot to pick it back up), so I'd start with buying a few of them when they are on sale.
I also make sure to refill my water bottle at night and leave it on my night table so I drink a lot of water as soon as I wake up. Remember, if you get 7 hours of sleep, that is 7 hours without any fluid intake. So, it is a good idea to drink in water as soon as you wake up. It's a good habit to get into and some people swear that by flushing out your kidneys as soon as you wake up, you'll lessen the chance of getting kidney stones.
A lot of people will tell you that the easiest way to reduce the calories you take in during a day is to not drink any calories. Skip the soda, sugary sports drink, etc... just drink water. I keep a few bottles of flavored seltzer around and that helps me get past any cravings for soda. After drinking seltzer water for a few days, you'll likely find that soda tastes ridiculously sweet!