I'm a senior and i started September 9th! Just have a lot of fun but there are many events like prom that are gonna cos a lot of money so save up! Also make sure that if your applying to college that you get organized and know when applications are due!
i'm moving into my dorm today, scary how that changes :o my advice, don't take your senior year for granted, it goes by faster than you think! just relax and have fun, you won't regret it :)