My copy editing textbook calls commas something along the lines of copyeditors’ worst nightmare, so you’re not alone there. I’m probably going to misuse some commas in this reply, but this is Reddit where I never write how I would formally. Commas are complicated (there’s a reason that there are jobs that, among other things, look for comma errors), but understanding the general rules is probably more in line with what you need. I’d say make sure you’re especially aware of what a comma splice is. That’s where a lot of trouble seems to come from, from what I can tell. Otherwise, there are many websites that have information about general comma use for free which can help you get the basics down. The Purdue owl has one, but looking at it I found it a little too technical and unapproachable. I’d say look for websites that give examples so you can see a model and understand what, say, a dependent clause is.

As far as essay writing goes, have you tried reading your essays out loud to yourself to see how your words flow? An alternative is to make a second document and rewrite your entire essay there if you’re like me and dislike reading out loud. Either one forces you to comb through at the sentence level. More work, perhaps, but better insight. This might help with your commas too, because a comma generally goes where you take a pause (but don’t take that as a rule).

I’m repetitive myself, but what I do is write my heart out and then go back and scrutinize. Force each word and idea to count. Make sure they add something new that you haven’t said before or, if you are repeating, that it’s intentional. Repetition isn’t inherently bad. It can help you come full circle or connect things. It’s just something to be done intentionally. And you need to force yourself to support why it’s there.

Another big thing for me is making sure my essay has good structure. Have the topic sentence specifically relate to the body text. Have paragraphs flow together. In the text itself, try to link sentences together such that the content of one sentence is related to the next (so basically don’t do what I’m doing in this paragraph which is written very choppily). Introduce and make sure to explain quotes and why you’re using them. Have everything go back to your thesis or main idea. Don’t be afraid to play around. Move text. Rephrase things. Do what you need to do to get some organization and keep it. I find it’s so much easier to write when I know how I’m organizing things. If I say that this paragraph will be about x, it’s so much easier to write and revise because everything has to come back to x somehow.

Honestly, check out your school’s writing center. First, it’s free. Second, they’re human, so they can give you a variety of feedback. They can help you to see the repetition and grammar. I know it’s some extra work perhaps, but what it sounds like you’re needing is some additional eyes on the paper. And that’s ok. I seldom write anything with having someone else look it over who can point out when my wording is awkward or unclear. Even emails. Reddit posts are the exception lol. Besides, we learn essay writing by doing. Then we hear back about works and doesn’t work. And we adapt. Nobody writes perfectly.

Or talk to your professor. They shouldn’t just be a grade distributor. They’re supposed to facilitate your learning. You just need to ask for it and try to use what feedback you get to improve. (To the professors in the sub, don’t accuse me of using the customer service model or being entitled. I’m just saying op should try to make the most of their education and show up to learn). If you’re confused, try their office hours. I’ve only had one jerk humanities professor who I would never go to their office hours again, but all of my other ones are very keen to help students flesh out ideas and improve. They can’t fix everything immediately, but they can help you to understand what’s not working and what strategies you can take to get better. This is done better in person than on paper or in print, because you can respond in real time and ask questions/for clarification. There’s no shame in asking for help. Literally, I always chat with my professors or my dad when I’m writing something, because I always get stuck and need to bounce ideas off someone and get out of my head. It helps me a lot in the end.