Think of it this way: The title MUST deliver on a promise. If folks are saying your title doesn't match your book, then they're probably right--it's not delivering on the promise it's set up for your book. Any film, or book or mime troupe or TV show or cartoon strip that doesn't deliver on that promise risks losing its audience altogether. ^ Best advice for choosing a title I've ever read.
For instance, if I go see a movie called, "Bill and Ted's Excellent Adventure," I expect, if nothing else, to see an excellent adventure.
John Vorhaus has an excellent exercise in his book "The Comic Toolbox, How to be funny even if you're not" about brainstorming for titles.
Just come up with some random titles, and practice asking yourself what sort of promise these titles imply.
Out of Her League for instance, might suggest a long-suffering, sympathetic female lead who has trouble coping with the challenges of work and family and a 1975 Dodge Dart that stubbornly refuses to start.
A Most Devout Coward is the title to my comedy novel about a devout Atheist who suffers OCD and social anxiety, witnesses a mob hit in a Manhattan Diner and now must enter witness protection and become a Priest. And I must say, I'm extremely proud of that title.
My titles usually come to me during writing or before, and then I develop the premise around the titles, but you can reverse engineer it and lay out your premise for your novel and then list the predominant elements of that premise. Once you do that, then brainstorm and write down every single idea you come up with for a title. Remember that with the Rule of Nines, nine out of the ten answers you come up with will be complete and utter shite, but there will be one golden nugget that will resonate with you. And if not, then keep making lists of tens of names until one does hit you. Don't try to make it funny or dramatic or TRY to do anything to it. Simply allow your mind to wander and write down what comes. Don't try to edit your choices, just let them rip, no matter how stupid and ridiculous they are. You'll know it when you find it.