The general rule of thumb is that to lose weight, one should consume 200-300 calories under their maintenance calories; some studies say up to 500 below is sustainable and effective . The tricky part is sorting out what your maintenance calories should be, and requires An honest assessment of your caloric needs and activity level.
A calorie/macro counter like MyFitnessPal, while not absolute, can help you ballpark your needs and keep an eye on your intake.