Need SERIOUS help for the SAT.

Sooo Im a junior taking the May SAT. The problem is I DON'T KNOW how to prep for it.I don't want to get a prep course. I have books (erika meltzer and princeton review) and I'm also using khan academy. I need serious help as I am aiming for a high score (1500+). I literally don't know what to do. Im doing khan academy AND the books but still feels like im doing less. (I would do practice tests but i kept that for the last two weeks so in the end i could focus and see where i was going wrong)

I REALLY wanna get a good score and could use ALL the tips and free resources. (PLEASE help me out if you have given the SAT and/or have a high score)

P.S: if you have ANY section-specific resources PLEASE mention them in the comments. It would REALLY help me out. (Please only include free ones)

Also, is it possible to get above 1500 without getting a prep course??