Another sneaky way to bag a good deal is to book off-season. Many resorts and hotels aren't as in much demand during these times, so they lower their prices considerably. This might mean booking when it's a bit chilly or when the kids have just gone back to school. Weekdays are another excellent option, as most people will have to work. Different countries have different off-peak seasons, so do your research.
Another upside of booking out of season is that there are fewer crowds. As a result, you won't have to deal with packs of loud tourists, and you can enjoy the sights without interruption.