There are virtually thousands of Travel Agents and an equalnumber of travel websites/portals offering you cheap and economical FlightTickets. Most big time travel agents and travel portals have some sort oftie-up with certain airlines.  They gethefty discounts on bulk purchases which most pass on to the customer. If youtake advice of your friends, they will suggest you to some travel portal theyhave recently been to.  But most peopleare not aware that the travel portals and travel agents that are around aremostly specialized in one way or other. Some are specialized in Domestic Travel, some other are specialized inInternational Travel, and yet some other are specialized in Last Minute flighttickets.  This means that the travelagents or travel portals that are specialized in something can provide you withbetter fares for that category of travel. 

Monday the first working day is the busiest of alldays.  Tuesdays, Wednesdays and Saturdaysare the best days for travel, as fewer people travel on the week days and hencetickets are cheaper, be flexible with your travel dates.

Try opting for odd time for travel that fewer people prefer.This way there won't be much demand for this kind of flights and hence arecheaper.

One way flights cost as much as round trip, so it makessense to buy your for a round trip if you are planning to return to your origin.

Try going to the airlines official website directly, sometimesthe airlines have discount offers going and they prove to be much cheaper thanthat of travel agents. 

Be aware and keep yourself updated throughnewspapers, magazines, internet and other media about discounts and offers. Sometimesairlines sell their own tickets bypassing their usual track going throughtravel agents web portals. These fares can be a lot of cheaper than what travelagents can provide you with.

If its not urgent,it is always a good idea to book your tickets in advance. Reserving at least 21days a head, book your tickets even earlier for holidays in festival seasons,particularly in November and December  Keep in mind that holiday 'blackout periods' mayprevent you from using frequent-flier miles.  

Before concluding I would suggest you to do a little onlinesurvey of at least 5 travel portals to search for the cheapest fare.