If you don't have a trusted person to spot plot inconsistencies and other errors, there are a few tips to clean your manuscript before submitting:
First off, forget about the manuscript for a few weeks before you start with the editing-process.
- Try to read as a reader, get the distance from the manuscript.
- find and delete adverbs(-ly). Only use them in moderation.
- Change as many -ing forms as possible; i.e. was standing into stood
- If you have two people in a dialogue, get rid of all the 'he said', she said' where it's clear who's speaking.
- Do not try to replace 'he said', 'she said' with other words for there is nothing wrong with it.
- When one character is addressed personally, don't forget to put a comma before it.
- i.e. 'That's what I meant, Gary.'
- And: He turned to Gary. 'Gary, do you think it's all right?' No need to address Gary as it's clear that he's been spoken to.
- Try to be logical; i.e. in the complete darkness he saw two figures. When it's completely dark, how can he see at all?
- Reality check: are your characters acting realistically? Is it believable?
- Spot repetition. Have you a habit of using the same phrases over and over? Change them.
- Plot inconsistencies: Is your MC just falling asleep and two paragraphs later, watching telly in bed?
- Does your scene drag? Does it feel unnecessary to 'tease' the reader for that many paragraphs? Delete the dragging part.
- Are there scenes that don't add to the plot? Chapters even? Delete them.
- Are there characters that don't play an important role in relation to the MC or story? Get rid of them.
- Is there a character that is not described much, though s/he is important? Flesh it out.
This needs some time to adapt to, but with every chapter it's going to be easier and with every book you'll become more secure if you learn these by heart.