Time also plays a factor. I had to cancel a planned spring break trip to Austin, TX, as well as Fort Worth, TX because I made a decision back in early January to hold off on buying tickets for two weeks.
Big mistake. The flight costs shot up over $100 the day after I made that decision. Total cost of the trip by air is now sitting at around $500-$600. I had budgeted $300.
The earlier you plan a flight, the better, ESPECIALLY if you're planning to fly internationally. Flight offerings are normally shown at least a year in advance, and that is when you'll probably get the best deals for them.