Titles are an important piece of your marketing. You want them to encapsulate your entire book in a brief and catchy way. Some authors are great at picking titles and for other authors titles are an afterthought. If titles don't come naturally to you, here is a technique that I have used before to choose a market-focused title that accurately represents the book.
Step One: Building Blocks
Before you try to come up with a brilliant title, I recommend starting out by brainstorming words that could be used in your title, rather than a complete title. This removes some of the pressure and helps you figure out what information you want your title to include.
Your brainstorming can be done as a group if you have beta readers, coauthors, editors, marketing people, or other teammates to work with, but it can also work for one person as long as you take breaks and come back with fresh eyes.
When you brainstorm words for your title, focus on making a long list, rather than a brilliant one. You may end up with a list of very stupid ideas at first. That's okay. Judging your list will come later. This stage is meant to be inclusive. Putting your self-proclaimed dumb ideas into the list may inspire other options or just get the creativity flowing. If you come up with a better idea later, add it to the list rather than replacing the old word. It will be easy enough to remove bad options later on. For now, a long list is better.
So what kind of words should be on your list?
Genre:
The first thing I recommend listing out are words related to your genre. Make a list of elements of your story that hint at the genre. For example, your fantasy novel might contain castles, dragons, magic, and royalty. A romance novel might include a handsome and mysterious love interest. A crime novel will include a crime with specific details and some kind of investigator.
Focus on anything that is tied into your genre and audience. What are readers going to get from this book? What does it have in common with other books in that genre or subgenre? What things take up the most time and space on your pages?
Include both specific details and general terms. Your list can include royal titles or job titles for key characters, important setting details, powers or technologies used in the story, or even items that are genre specific, such as swords and space ships.
Conflict:
To add to your list of genre-related words, I recommend listing out words that have to do with the conflict in your plotline. This can provide a lot of great verbs and adjectives that pair well with the noun-heavy genre elements.
Is your book about secrets? Battles? Politics? List synonyms and specifics. You can also list tools like swords, computer code, or heartfelt chats, if they are used in the conflicts.
You may want to list words related to the goals of the main character or what is at stake during the conflict. For example, Game of Thrones is, at its heart, a story about people trying to take over a kingdom and win the throne.
Hook:
The last category of words that you'll want to list out is words related to your hook. These may have been covered by the genre and conflict lists, but if not, write those words down now. This can include words that are part of your elevator pitch or words that hint at a writing style or setting that readers will be excited about.
Step Two: Piecing a title together
Once you have a good long list of building blocks, you can start combining the words in your brainstorming list together to build complete titles. Don't aim for a brilliant title yet. Start with a judgement free list and dumb ideas. You're more likely to hit on a brilliant title by listing lots of possible titles than sitting and waiting for just the right title to occur to you.
Combine your building blocks into pairs or phrases. Try options of different lengths. Title can be one word. They can also be six words.
Play around with the structures. You may start with "a" or "the" or you may want to stick to only dramatic words. Try some possessive phrases. Try a noun and an adjective. Try out a title with a verb in it. Variety in your list will help you get more creative.
Don't be afraid to be repetitive. There can be a huge difference between The Chronicles of Narnia and The Narnian Chronicles. List both options and see what other ideas those titles spark.
Step Three: Narrowing It Down
After you've made a list of possible titles, make sure to take some space from it. Leave it alone for a bit so you aren't in the same headspace as when you made it.
When you're ready, pull out the best options. Don't delete your longer list, but make a short list with the most interesting and promising titles.
Find titles that are built from words your readers already know and not just words that you've created for your world/story. Even if readers don't know what The Hunger Games or the Mortal Instruments are, the names are made out of words that readers do know and hint at the meaning without any additional context. On the other hand, Katniss and Clary, while important characters, have names that mean nothing to readers until they've read the book. "Katniss's Bow" would not have been as compelling of a title as The Hunger Games because it doesn't tell the reader anything about the book.
Step Four: Finalizing the title
Once you have a handful of favorites, it's time to think like a marketer. Judge each title as a tool to help readers choose your book. Does that match the tone of your book? Can you tell what genre it is? Does it seem like it could be any other genre?
Ultimately, you'll have to choose a title that feels right to you, but including an outside perspective can be a huge help. Random people on the internet won't have the same context that you do. Make sure your title doesn't have any weird connotations or meanings you don't intend. Additionally, an outside perspective can tell you what your title will indicate to random strangers, which is really who the title is for.
Ideally, using this method, you end up with a title that is cool and also helps readers get a sense of what your book is about.