Having a budget and knowing what you will spend if you can locate the flight for that price will save time and could save money as opposed to waiting too long and paying last minute prices. By having an idea of what a good price for the flight is and taking the time to check early and often, you can find the perfect flights.
The main thing to remember when trying to find the cheapest flights is to look a few times before you book. Even looking on the same website the price may change over the course of a few hours. By being flexible, knowing what you will consider a good deal, and comparing with frequency you can find the absolute best deal on flights.