Try to buy somewhat in advance. It gives you the opportunity to look for deals.
Sign up for airline emails, they will send their own internal deals. I live in Canada and Westjet sends lots of deals. I made lots of weekend vacations out of $60 plane tickets ($200 with taxes).
Search deal websites. Redtag.ca is a Canadian example. Hotwire.com etc etc.
Collect Aeroplan or Airmiles points. You get basically get a free short hop flight for signing up for an Aeroplan credit card.
I use my collected points to buy flights and then sell other flights to my friends for a deal and I get some spending cash on the vacation. Win win.