When can i take the SAT test and how should i prepare for it?

i just finished junior year and i'm going into my senior year of high school. i need to send my college applications in between this September-December so i'll be sure that i'll be eligible for most colleges in my state. when does the SAT start up again? i wanna get it done as soon as possible, and how should i prepare for it? I've never been very good at school especially when it comes to math (algebra and geometry) and essay writing for English...what can i do over the summer to prepare myself? advise? tips? oh! and is the SAT test hard? thanks!!!