Read your manuscript aloud from start to finish. You will hear mistakes. You will find awkward sentence structure, names that are more difficult to pronounce than they are to read, unclear references, holes in scenes, etc.
Read aloud. Fix it. Repeat.
Reading your manuscript aloud is the second best self-editing technique.
The first best self-editing technique is to read your manuscript aloud to someone else.
When you read aloud to just yourself, you tend to tune yourself out. But when you read to someone else, you notice every single word.
This is why a good critique group, where you read your pages in front of the group, can be so powerful.