I think the keys to SAT prep are: 1. knowing the test and how to approach it. and 2. Practice.
For #1, I suggest the book Up your Score; the Underground Guide to the SAT. https://books.google.com/books/about/Up_Your_Score_SAT_2018_2019_Edition.html?id=kWAVDgAAQBAJ
It was written by a bunch of kids who got perfect scores on the SAT, and it’s all about strategies for taking and beating the test.
For #2, I suggest either any SAT book on the market-- Barrons is fine-- and one hour a week to start. Do at least one section per sitting. When you’re done, take a look at the answers. But, more than that, take a look at the grid at the end of each test that tells you which type of problems you’re getting wrong, and keep notes. After a while, you should start to see some patterns-- you always get the circle problems wrong, or the statistics ones. That will point you in a direction for future prep.