Hi, Hopefull!
Okay, one of the first things you need to do is think of a PLOT. No, I'm not being sarcastic. It's actually one of the most difficult things for a writer to do. If you've started your book eight times and are getting stuck, what might be happening is that you're hoping ideas will come to you as you write. But you might not be that sort of writer. There are two primary types:
One is called a
Plotter. A plotter is a person who needs to think through the elements of the book until they make sense. Every element, from hair color to eye moments to dialogue is plotted out on note cards, or Post-Its or on a pad before the writer ever sits down to actually write the book. It takes a plotter longer to start a book, but it goes very quickly afterward. When the book is completed, it's fully formed. Very few edits are needed.
The other type of writer is called a
Pantser. Weird word, I know. But it's short for "Writing by the seat of your pants." This sort of writer only gets the ideas DURING the writing process. If a Pantser tried to organize the plot, and write it all down, once the end was reached, it would be over. The book would never get written because it was . . . well,
done. No need to write any more about it, and on to book two. Often, a pantser's first draft will be very short because the GOAL is to get the basic plot down. The details will get filled in later, over multiple drafts.
So, you might consider what you think would be a good plot. Since you're eighteen, what has happened to you or a friend that would make a good book? Or, instead --- what would you LIKE to do? How would your hero react to, for example, winning a contest that would send him and two friends on a trip to another country? What would happen once they got there? Would they get involved in intrigue like stumbling into a robbery and getting blamed? Who would they meet while they were trying to prove their innocence? Etc., etc. You can see how many directions it can go.
So, don't worry too much about using ONLY your life as a guide. Let yourself dream a bit and imagine possibilities.
Good luck!