That's always a tough question because it's so individual. You could track how many calories you are eating now in a week. If you're maintaining your current weight, then you'll want to reduce the number of calories by, for example, 7000 in a week (1000 per day) if you would like to lose a healthy 2 pounds a week.
If you're really eager to get started now, then pick a reasonable number like 1600 - 1700 calories and see how that works. If you lose on that amount of calories, then stay there until you stop losing regularly, then lower your calories by 100-150. Make sure you're eating quality calories because quality really does count. Add some exercise in to make you burn even more calories.
There are some guides on the internet (I think shape.com has one), but the information I've heard is that they're not that helpful. However, they might be a good starting point for you.
My advice is not to start off too low because, if your weight loss stops for some reason (the dreaded plateau), then you have no way to drop calories without endangering your health. You want to lose at the highest number of calories you can so that you can maintain at the highest number of calories possible. Starting at a number where you lose a reasonable amount of weight, then lowering that over the course of your weight loss is a sensible plan. Good luck!
Women who behave rarely make history.