@Alexx04
It is my experience opinion that one you have written something, you should have another writer you respect and know personally (or just respect) read it and tell you their thoughts, then you should go over it and fix any major mistakes that were pointed out to you. During that time, you usually find a few on your own and fix those.
This process is much easier if you have your writing in a Google Doc or something similar where you can share it with a person who can leave comments or suggested revisions for grammar mistakes.
Which leads me to my next point.
You should always have another person edit your writing. They are sure to find mistakes that you either didn't know were bad, or you just wouldn't have noticed otherwise.
And we all make mistakes, so it's definitely easier if it is someone you trust and know have the ability to edit your writing in a way that is compatible with your own writing techniques and skills.