Kill Them Off
At the end of the book, kill off your main character. This prevents your character from coming back and demanding more stories from you. Nothing is more annoying than a character who does not realize you have other tales to tell with different people. If you do not do something about such character, they will sit beside you and drone on for hours about other adventures they have for you to write down.
The solution to this is to kill them off. When their story is finished, find some really interesting way for them to kick the bucket. Make it worthy for your readers to give them proper closure, as you do not leave the reader hanging. Maybe the villain was not quite and dead as everyone thought and grabbed the character before they both tumbled down into the lava. Or maybe they had a terminal disease which overcomes them in the last few pages. Or maybe they sacrifice themselves for someone they love. But when you are done with a character, kill them off so they do not bother you again.