Check out Air Asia for some amazing flight deals. A number of times a year they have promotional fares and this is the time to get in quick and bag a bargain.
Register as a member to be notified when these deals come up.
However a few more things will help you to be sure of picking up one of the promo fares.
First of all explore their website and study the route map to find out where they fly. Pretty much all their flights route through Kuala Lumpur. So for example if you wanted to fly from Melbourne Australia to London England you would have to book 2 seperate flights, Melbourne to KL then KL to Stanstead. Whilst Stanstead is not strictly London there you can get from the airport to London Victoria coach station easily using Easy Bus with fares as low as GBP 2.00 if you book early.
Check out which days and at what times the flights operate on your chosen route and have all this information ready for when the deals come up. Generally mid week flights have more seats available at promo fares and it helps if you can fly a few days either side of your choice date.
Now as soon as the deals go on sale get on line and start checking out your options and if you don't find a promo fare straight away then move forwards and backwards by at least a week to see if they are only on offer on certain days. Not all flights have promo fares so you could just be unlucky but during the last sale it was possible to buy a ticket from Melbourne to London for Aus$406 one way including taxes so it is worth spending time playing around on the site.
We have taken 10 flights with Air Asia and they are superb value for money, but remember to some extent you get what you pay for and no matter what you do during the booking process you always seem to end up paying something extra - we travel with carry on baggage only, don't require meals or seat allocation but still got hit for a credit card fee! Let me know if you ever get round this please.