One piece of advice: Don't
drink your calories. That's where a lot of people get hung up. They set a certain calorie limit, and then forget to include the Crystal Lights, juices etc that they consume. Right now, I drink mainly 1 cup of orange juice with breakfast, and then water the rest of the day. On the weekends, I treat myself to a few (not many) 100 calorie cans of Coke if I feel like it. Otherwise, it's water.
As much as it looks tempting and easy, don't fall into the pit of buying those Lean Cuisine or other frozen meals regularly. Once in a while isn't bad, but I personally found that for 300-400 calories, they still didn't fill me up.
Do look for low calorie but highly filling foods for snacks. One of my favorite snacks is a package of frozen edemame from Costco (they come in a box) that contains 100 calories. It takes about 15-20 min to eat them because there are SO many. And they're filling.
Enjoy fruit, but don't go too over board right now on it. I do more vegetables than fruit because I feel vegetables fill me up more.
And once you have a set number (1500, 1800,whatever) make sure you're reaching it. Don't eyeball that peanut butter, measure it out into a tablespoon to be sure. Little extra calories add up and soon, at the end of the day, you may have added on 100 or more calories just by not measuring.
I also found it's helpful to plan your meals out a day in advance. When I get home from work around midnight, I sit down for about 10 minutes and write down in a Wordpad what my next day will look at. Breakfast, morning snack, before dinner snack, lunch/dinner, evening snack, bedtime snack (if the calories allow). This way I stay on schedule and on goal.
Oh, and because I work an incredibly sedentary job that really doesn't require you to get up at all in 8 hours, my calories are 1400 and under, but no lower than 1000. I also know I have a very slow metabolism, so anything higher would just make me gain weight.