there are also 2 other tips i was told about, however not sure how they work with each individual airline.
1. just prior to booking, make sure your cookies are cleared on your pc. i have tried this with a few of the 'normal' web based airlines, and suprisingly returned lower fares.
2. do not put in the exact dates you want to travel - instead try putting a day or 2 either side and then just select the correct dates from the selection offered (check earlier / check later). someone told me that they always do this and generally get cheaper fares because on the dates that you request - because the airline thinks that you actually want 'these dates' will offer a higher fare than the alternative dates. not 100% sure about this, but might be worth a try.
regards