A while ago, a fellow author was asking friends for potential book titles for her novella. We chatted online and I mentioned that titles were difficult for me to come up with. After thinking about for a bit, though, I realized I was wrong. Titles are kind of easy for me. As to whether I will ever use them is a different matter.
Book titles aren't copyright protected. That's why some books have the same titles. Trademark protection is different; that's why your newest novel can't be called Harry Potter and (insert rest here). But phrases that are general, say One Moment In Time, is fair game.
Most of my title ideas come from other titles and song lyrics. If I'm going to use something like that, I make sure my work is of a different genre than what the original title came from. For example, I have a potential title: Beauty 7. This was originally the title of an old Japanese drama dealing with the lives of the employees and customers of a beauty salon. I think it would make a great title for a horror/mystery story about someone killing seven women for their body parts to create his idealized girlfriend. Same title, different genres.
If you have a certain set of lyrics or phrase you like, there is no problem using it. I write down titles as they come to me, sometimes I get an inspiration for an idea; most of the time the title just seems cool and I wait for a story that fits it. Even titles of TV episodes can be used.
If you're unsure about using a title for a book, possibly for legal reasons or it quite doesn't fit the story, think about saving it for a chapter heading. Not all chapters have to be Chapter 1, Chapter 2, and so forth. While thinking of a title for every chapter might be more difficult, it can help get you use to thinking about titles and you can use ones that you've been kicking around in your head but weren't quite sure about.
If some word or phrase strikes a chord with you, write it down. If you have an e-reader and a particular passage or turn of phrase catches your eye, highlight it. You never know when the right title will come along.