Tip of the Week: Immerse yourself in your subject.
Now when you are writing a book that requires lots of research like nonfiction or a historical novel, you obviously have to learn all about your topic. If you don't, you will have a hard time writing a convincing book.
But even if you have written a contemporary teen mystery, you should be well versed in other books in that genre. Not only do you need to know the competition, you also need to know what others have written so that you can modify your story to keep it from being too similar.
However, you do have to be careful that you aren't overly influenced by the books you read. You don't want to subconsciously be plagiarising someone else's work. So, I recommend reading similar types of books before and after you write your work, but saving comparable works in your genre for the editing phase.
For example, if you are writing a midgrade mystery, read some adult mysteries while you are planning and writing your book. This will acquaint you with mystery conventions without directly influencing your work. Then, while you are editing, read a few midgrade mysteries to see how other authors handle issues that are unique to children mysteries as opposed to general mysteries.