Booking my first holiday, need advice on how to find the best deals?

I'm booking my first holiday for 2, we are wanting to go to Tenerife or somewhere else in the Canary Islands, we are looking at January/February time for my birthday. Ideally All Inclusive. I havent been on holiday in 9 years and at that time a travel agent did everything for me, so I really dont know the tips and tricks.

Any tips on how to find the best deals? Such as how to find the cheapest day to fly, what websites etc etc. Thanks!