Worst time to shop for flights in on the weekend. They know people have free time and are trying to do vacation planning, so the fares go up. Best time to shop for flights is Tuesday afternoon - Wednesday afternoon. Usually, one airline will start discounting flights on Tuesday morning and the others will follow suit to try to match fares over the next 24 hours. The cheapest flights will be on Wednesdays and Saturdays and the highest fares will be for flights on Fridays and Sundays.
When looking for fares, start looking as far out as possible to get a general idea of what the "usual" is. There was a recent article that said some blog tracked flights over an extended amount of time and found that the best fares to be had were at about 6 weeks out. But if you start looking early, you'll have an idea of what is and isn't a good fare for a particular route. The worst times to book are less than 2 weeks before your preferred flight date.
Good luck.