I read at a travel site that airline ticket reductions are steepest on Tuesday, leading into Wednesday morning. When I booked my flight to San Francisco for last month's ad:Tech I got coast-2-coast tickets for $137 in February when booking on a Wed. morning.
You should book at least 30 days in advance, and expect to pay a premium this time of year because it's the height of the travel season. I think July and after you will see lower prices. Also, expect to pay a fuel surcharge, which also will be lower in July.
I generally check many travel sites for deals, like Travelocity, Orbitz, Kayak, Expedia, etc. before I book, but found the lowest priced tickets at the AA website. I believe AA is not promoting themselves at third party sites anymore.
Be sure to sign up with airline miles programs and don't lose the member numbers. I was able to buy a hotel stay for Affiliate Summit Las Vegas using airline miles from Delta. Also, most hotel chains have membership clubs that pay points, and I collect those, too.