for the writing & language section, the best book to study from is #college-panda . also, the writing and language quizzes of khan academy are very good. just, don't use that website for reading practice.
one of the best things you can do to improve your verbal score is to work on vocabulary. that is, learn more and more words that you may encounter in the exam
so, a good way to do this using vocab flashcards. you can prepare your own flashcards or there are several options on amazon that you can buy, like this one:
you can use digital flshcards that are provided by xome phone apps like this one:
you can use this app to study vocabulary in flashcard format:
the khan academy has excellent resources for writing &language prep. the writing and language quizzes are brilliant! here:
www.khanacademy.org/mission/sat/practice/reading-and-writing --you need to sign up first--
there are some tests here as well. but, i don't like how they are organized. you might still find some useful stuff : www.cracksat.net/index.html
especially for the writing section, the book by steve dullan is a great resource. the punctuation and grammar rules necessary for the exam are perfectly summarized. in fact, there is no other book in the market that does a better job in that respect.