Obviously price drops depend on a number of factors. How far out your date is, how many seats are booked on the plane already, the price of competing airlines on that route, etc.
This week, I ended up having flights that dropped on Tuesday afternoon, drop again Wednesday! These are flights that are 4 weeks away. I guess Delta realized they weren't going to fill that flight in a few weeks with a price of $555! I got it for $304.
Another tip - if you are booking for more than 1 or 2 people, price the tickets for 1 person and then do another search for the full number of people in your group. This is a strategy for flights that are almost full, around holidays, or sometimes your tickets just push it over into the next price level. For example, if I could get one ticket for $300, but when I type in that I need 3, the price jumps to $350 each. Once you've crossed into that next price level, the airline will charge you that for all 3. But if you're willing to book separately, you can get the first ticket for the lower price and just pay the higher price on the remaining tickets. I play around and see if I can get two tickets for the lower price - or however many you need - keep plugging in different numbers to maximize the number of tix at the lower cost. This works for us as we are okay to have one of us sitting separately and one of us with DD. And sometimes you may get lucky and will be able to be seated together anyway!