I second jackrabbit14. I scored a 1960 on a practice test in October, and scored 2130 on another practice test I took yesterday with virtually no prep in between (besides browsing through the Blue Book and some grammar rules in Erica Meltzer’s book). Your score really can fluctuate inexplicably, depending on the day. I will also be taking the SAT in October, and, if I need to, in November.
What the posters above have said is true: statistically, it is very difficult to raise your score 400+ points. However, it is certainly a manageable goal, assuming that you are willing to dedicate a lot of your summer to studying (and I mean STUDYING, not browsing social media, etc.)
For the writing multiple choice, purchase Erica Meltzer’s Guide to SAT Grammar. This helped me improve from a 61 PSAT writing score to a 760 SAT practice test score (Assuming I got a 10. If I got a 12, it would have been a 790). Make sure to do lots of practice tests from the College Board blue book, and go through your mistakes when you are finished, marking which grammar rule you misused for each question you got wrong.
For the essay, there is an excellent thread right here on CC named “How to Write a 12 essay in 10 days.” Google it. Read it. Embrace it. Also, practice is key here as well.
For CR… I’m not one to give much advice. I’m still stuck below 650 for that section. There are some good threads on CC for the passages. For vocabulary, however, please don’t listen to people who tell you that you don’t need to memorize words to do well. No “strategy” can beat simply knowing the words. Besides, if you know the words, you’re doing yourself a favor by giving yourself more time for the passage reading, instead of deploying unnecessary, time-consuming strategies for sentence completions. I recommend Direct Hits 1 & 2. The 1000-3500 word lists are a waste of your time if you’re only trying to get up to 1900.
For math, I would really recommend that you take three math sections from the Blue Book, see which types of problems you commonly got wrong, and focus in on those areas. Instead of wasting time by going over everything, pinpointing exactly what you’re messing up and training yourself to fix those errors will be extremely beneficial. Also, remember that SAT math is not “hard.” It is TRICKY. Always underline what the question is asking, and make sure that you’re answering the right question when you come up with a final answer.
The above is probably nothing new for most CC’ers. I just thought it would be nice to summarize my findings on CC to help out this individual. Good luck!