If you're flexible on dates, try flying on Tues, Weds, or Sat to get the lowest fares. And, if possible, try booking at least 2 weeks in advance to avoid higher fares--and even earlier during busy travel weeks in the summer.

Additionally, JetBlue is the only airline that flies LGB to Washington nonstop. If you're limiting yourself to nonstop flights, you don't have much choice in the market. You may want to consider 1-stop flights on several airlines and/or nonstops to other LA-area airports to search for the lowest fares.