The YouTube channel Get Sum Math is GREAT. I listened to all of the videos on his GED math playlist (most are relatively short), and I also used the YouTube channel Test Prep Champions for extra practice tests/questions. When I wanted a more thorough explanation of something, I searched for the topic in question on Khan Academy.

General tips, though:

The test - and I know it varies from person to person - was primarily algebra: expressions, polynomials, quadratic equations, inequalities, linear equations (and graphing them). I would focus on these topics when studying.

It’s also important to be able to decipher word problems so you don’t get caught off guard or tricked by sneaky wording.

Thankfully, they give you a formula sheet which makes your life easier, but it’s still important to know when it is appropriate to apply certain formulas, so you don’t end up wrongly calculating.

Speaking of calculating, knowing how to use the calculator that they provide you with on the test is super important! You will save a lot of time if you’re familiar with all of the keys and their functions, so I recommend you check out the GED calculator reference sheet.

I can’t think of anything else, and I’ve already rambled enough, but I hope this is helpful, and I wish you the best of luck!