Well, I tend to look for value first and foremost except, of course, when junketeering on company expenses.
That being the case, the best deals are almost certainly to be found on the internet and there is an amazing array of choice out there. Then it depends on where you're going and how you want to get there.
I have booked a few different trips lately and have used a number of different tactics to make sure I am getting the absolute best deal.
For a flight to Dublin in December (booking in August with plenty of notice), the obvious solution was an LCC and a ludicrously cheap ticket. You want to scoop something like that up when airlines like Ryanair are doing a sale.
Booking London-Geneva for March next year was interesting. We go in a group and usually like to travel together from LHR
on a proper airline at convenient times. Solution was when Opodo were doing their mad Monday sales a month or so ago, with £20 off each ticket. There is a website which gives you cashback of 1% or up to £5 per flight when you book through Expedia, Opodo or Ebookers as well.
For any long distance a good surf through all the internet agents, the airlines, as well as flight-finder sites like Travel Jungle, is a must. Weekend travel supplements also give an excellent guide to what the best deals are. The best deals can turn up in any one of these ways and sometimes quite unexpectedly. I thought a bunch of flights at one price had gone altogether once the price increased on the BA
site but Expedia still had them all on special offer.
I was booking internal flights in Mexico recently and the usual channels seemed very pricey. So I went to the individual airport websites to see who flew to and from each one and found that there were small LCC equivalents who obviously can't afford to market themselves very well (eg Aerolineas Azteca) who flew for a fraction of the price of the main carriers. Similarly in Chile, where I lived for a while, you could be emailed weekly specials from LanChile of internal flight deals that were otherwise buried in their website. Sometimes these deals will only be in the national language too.
You really have to look quite hard for business and first class deals. I have stumbled across two excellent sources of bargains for this: one being Austravel for flights to Oz/NZ and the other being a legendary thread on a similar website to this that explains how to fly from a European airport back to the Uk and then onwards for a huge discount from a direct fare.
As far as upgrades go, I used to get one virtually every time with a lowly BA
Silver card even on the very cheapest (BA) ticket. This seemed to count for much more than the actual price paid.