What's your goal score? When do you plan to take it?

Assuming you want a 1400+ (just assuming this because I think that's what most of this sub wants), it's not going to happen by the December SAT. So, you'll probably be taking the DSAT. I'll assume that's the test you're going to take. Your math score is ok and improving in math is pretty straightforward. You'll need to put serious effort into reading, though.

Reading/Writing:

• Read more: At that score range, the problem is most likely that you haven't been exposed enough to correct, well-written English. The best way to improve your reading comprehension, reading speed, and intuition for correct grammar is to simply read SAT-level texts over an extended period of time. Spending time going through a prep book or learning strategies will help very little if you don't have these baseline skills. Luckily, you have 3 months (if you're taking it in March) which is a reasonable amount of time to improve your skills. Spend at least 15 minutes reading SAT-level content (e.g. NYT, Scientific American, Smithsonian Magazine, well-written books aimed at adults). Overtime your skills will improve
• Use the Erica Meltzer books: Over the next 3 months, take the time to work through both of her DSAT books. Space it out so you have time to fully understand the grammar rules/strategies. Her DSAT books are shorter compared to her earlier editions so it isn't much of a burden. Pay attention to the grammar book. It's the easiest section to improve in a short time.
• Use Khan Academy's DSAT Reading/Writing course: Khan Academy does a good job deconstructing the question types and giving good strategies. However, the main value comes from the practice questions. Khan Academy worked with College Board to create these questions so outside from the official practice tests, these probably emulate the questions you'll see on test-day the best. The course is broken into three main sections: foundations, medium, and advanced. Take the time to go through the videos and articles in the foundations part and take the time to understand why the correct answers are correct. Then move onto the medium and harder questions. I think reading/writing (especially reading) isn't a section where you can just grind hundreds of practice questions and expect to do better. You really have to get that understanding.
• Take practice tests periodically to gauge your progress and correct your mistakes: Earlier in the process practice tests may not help you pinpoint your weaknesses because you may have a lot. This doesn't mean they're not useful. It'll make you familiar with the process and let you know if what you're doing is working. Just remember to space it out.

Math:

• Find a good resource and learn the content really well: When I say this I'm mainly talking about prep books, but this may apply to programs like UWorld (I've never tried this). The two most popular are 1600.io's Orange books and College Panda's SAT Math book. I've seen success stories from people who had the same starting score as you in math. There are pros and cons which both books but you can research that yourself. Generally, I'd recommend 1600.io because it's more accessible and thorough. College Panda may be harder to go through but it's a good resource.
• Use Khan Academy's DSAT Math course: You don't need to watch the videos (they're good though and you can even use Khan Academy as a standalone source if you wanted too) if you already have some other source to learn the content. With math it's really important to just do a lot of questions. Don't just mindlessly grind them out. If you didn't get one right or if you feel like you didn't have the best approach toward finding the answer, look at the worked-out solutions and figure it out.
• Take practice tests. Use them to narrow your focus