Start preparing for the SAT/ACT during the summer after 10th grade and to take the test in August or September of 11th grade. This will give you plenty of time to retake the test if necessary before college application deadlines. This also prepares you for the 11th grade PSAT that you take in October. PSAT is not mandatory, no college will need the PSAT score, but a high PSAT score can make the student eligible for National Merit Semifinalist/Finalist or commended awards.
It's also important to note that you can take the SAT/ACT multiple times, and colleges have different policies regarding which scores they consider. Some colleges require all test scores, while others will only consider your highest score or will "super score" your reading and math sections from different test dates. It's important to research each college's policies regarding test scores to determine the best strategy for submitting your scores.
In terms of test preparation, there are many resources available, including online practice tests, study guides, and classes. It's important to find a study method that works best for you and to give yourself enough time to adequately prepare before taking the test.
Taking a practice test on Khan Academy is a great first step in preparing for the SAT.
Khan Academy provides official practice tests from the College Board, and it's recommended to take these tests as they are the most accurate representation of what you will see on test day. The practice tests on Khan Academy include the Reading, Writing, and Math sections, and the essay section is optional, so you can choose whether or not to take it.
After taking a practice test, you can use Khan Academy's personalized study plan to focus on areas where you need improvement. The study plan is based on your performance on the practice test and is designed to help you build the skills and knowledge you need to do well on the SAT. Khan Academy also offers instructional videos, practice questions, and other resources to help you prepare.
Score the test as per the scoring guide that came with the test. This is your baseline score.
While taking a practice test at a coaching class can also be helpful, it's important to keep in mind that the tests provided by these organizations may be more difficult than the official College Board tests. This is because they want to create a lower baseline score to demonstrate a bigger improvement when you take their training courses. It's important to use these tests as a supplement to the official practice tests rather than as a replacement.
Test prep books
Erica Meltzer SAT Grammar workbook
You can find older college board tests on reddit Released SATs
Spread out your college board 10 practice test till you take your last SAT/ACT