One thing to get started would be to see how much you're eating currently, without making any adjustments.
Track for a few days or so your intake and use that to set a goal for your new daily caloric intake. Check out
http://nutritiondata.self.com/ as a great site to get the nutritional info of most foods, including restaurants.
Once you've established a baseline, set a goal you can stick with. Say you're taking in 3000 cals a day now, shoot for 2500. The worst thing you could to is try to go whole hog and get down to 1800 cals/day right off the bat. You're body will revolt, you'll be miserable, hungry all the time. You'd be surprised at how much impact little changes can make.