There was a great Stack post on this a while ago. Basically it always boils down to booking early, really, that's how you get those cheap flights. The "book a few weeks before" option is bunk.

For most of us Europeans, jumping off at a stopover isn't an option, although it is possible to do this on trains sometimes (and actually it's very legal, you're entitled to break your journey at a valid calling point).

https://travel.stackexchange.com/questions/2952/flight-ticke...