If you're thinking about writing a novel, November is the month to start. NaNoWriMo (National Novel Writing Month) began with 21 college students in 1999 in the Bay area and has now developed into a worldwide experience with over 300,000 novelists and would-be-novelists participating in 2013. The idea is to write a 50,000 word novel from November 1 to November 30. So start thinking about a plot and a story. On November 1 (you can begin at 12:01) put pen to paper or fingers on the keyboard. Make sure you sign up to participate, you will get lots of encouraging e-mails, you can find friends and track their progress and have a fun month doing something that's perhaps been on your bucket list for years. And who knows you may end up with a best seller. By the way, plan to write 1,667 words a day to reach 50,000 words in 30 days.
Note: There are no fees associated with joining, but it's nice to donate a few dollars to keep the site up and running. They are doing a lot to help young writers.
Sites for plot ideas:
Overheard in New York
Plot Ideas from NaNoWriMo
Plot a Story
Plot Ideas to Run With
Note: Once you have an idea for a plot and have made some notes, don't spend a lot of time on developing it when November 1 gets here. The idea of NaNoWriMo is to just write and let your subconscious do the work. You can edit later. Don't look back over what you have written, just keep writing and writing and writing.