There are two things you should do:
- Wait long enough for your mind to get away from the ‘writer’s mindset and into the ‘reader’mindset. That way, when you read, it’ll be as if a reader was reading — and everyone knows that readers find all kinds of mistakes, typos, etc. If you are in ‘reader’ mode, so will you.
- Don’t just edit your work once. Every time you sit down to write, go over what you’ve already written— or the latest chapter/few pages/part if you are writing a long, long piece— to look for flaws or ways to say it better. Every time. No exceptions. I guarantee that each time you do this you’ll find something that you missed earlier. Do it. It’ll work.