For flights we always start looking if KLM is offering the destination where we want to go. If so, big chance we book here, because this is one of the better airlines. Two time a year the have the World Deal Weeks with big discounts. we will communicate you off courcse when they are.
A lot of the time Transavia has destinations that KLM doesn't have. Like Sevilla for example. And it is not really expensive. A quick tip. Most of the time they fly form the smaller airports on better times and for better prices then the larger airports.