It's hard to give a specific answer without knowing more about the book, but it is important that the ending feels satisfying and fulfilling. It should be a resolution that ties up all of the loose ends, and one that feels like a natural conclusion to the story. Depending on the type of book and the tone that it has, the ending could be sentimental, surprising, or something else entirely. Think about what kind of message you want to leave your reader with, and figure out a way to get there.