Don't waste time worrying about spelling. You can think about all these aspects of writing after you've decided what you are going to say. If you spend a lot of time fixing all the prepositions and conjunctions in an early draft you are not going to be willing to cut out paragraphs or sentences that you later realize aren't necessary, or to change them substantially. So don't put a lot of effort into proofreading until you are sure that what you want to say is the best you can come up with, then you can spend more time on fixing up the writing so that the punctuation, spelling, etc. is correct. More experienced writers rewrite more times and more substantially than less experienced writers.
Good writing takes time for everyone.
So give yourself time to rewrite so that your readers see the best of your thoughts and writing, not the best you could come up with at the last moment. Ask friends, ask professors, ask your writing advisor in languages. Good writing takes practice. The only person who can make you a better writer is you. So work at it, show your work to other people, and rewrite, rewrite, rewrite.