My doc told me there's a lot of debate around this. It also depends on his sperm. My friend was trying to get pregnant by having sex every OTHER day (that's generally what my husband and I do) until she ovulates. Then during ovulation we have sex every day for about three or four days in a row. My friend, however, and her husband had sex like three times a day for about a week and they got pregnant THAT month! I think it really just depends.
Most importantly.... just have fun with it. Have sex when you want to. How long have you been TTC? If you're just starting, I would say don't worry about it, and just have sex when you feel like it. Don't make sex a "job" until you have to!