Booking a flight can be a stressful thing to do, since no-one knows what a good price is anymore. With so many budget airlines going out of business, it seems that people once again have to pay more for their air travel. Despite this, there are ways to save money when booking a plane ticket, providing you're willing to be flexible with when you leave and when you come back (assuming you are booking a two way ticket).
What I mean by this is that the best (and cheapest) time to fly in the week is Tuesday to Thursday. This is because most people fly Friday to Monday, so you'll be booking tickets on flights that are usually only half full. As an extra incentive for people to book flights on these days, airlines often offer cheaper tickets. While this obviously won't suit everyone, and flying in the middle of the week can sometimes be more trouble than it's worth for some people, if you can manage it it's definitely worth it.
Another way of saving money is to book a seat last-minute (as in on the day of the flight). Some people might view this as risky, since you're taking the chance that the flight might fill up, but since there are so many airlines these days, each with multiple flights every day the chances that you'll find one are still extremely high. The reason last minute seats are so cheap is because they are worth nothing to the airline company once the plane takes off (if they're not filled), so they might as well take whatever they can get for them.