It doesn't sound like you're ready to write any books about arduino projects. Come back when your post count is 2000 - 3000 or higher and you won't need to ask us because you'll already have about 500 projects to write about. If you want to start a project or pick a project or troubleshoot a project , feel free to post but I really don't see why you are asking us when there's probably at least 10 years of projects at your finger tips on the forum. Just start reading. It really is just that simple.