Finding objectivity is one of the hardest things we do. I don’t think any writer can ever become fully objective about her work. Putting it away for a month and not looking at it helps.
Then – before you read it – give it to three trusted readers; people who read a lot for fun and respect you enough to be honest. (DO NOT give it to relatives or lovers!) Ask them to read it and write down the three aspects of the story that are working the best, and the three that are the most confusing.
Next: take a copy of your story to a new location; NOT where you wrote it. Go to an independent bookstore, a coffee shop, a park, a nice hotel lobby. Read their comments first, then read the manuscript. If you can’t find anything you want to change, you’re done.