Proofreading is an important part of your work. It is imperative that you check every word, sentence, and punctuation mark to make sure that your message is getting across clearly.
Here is the thing not to forget: You need to check more than just your story words.
Make sure your title and chapter titles are correct. Make sure you didn't accidentally follow chapter seven with what you called chapter six. Check your table of contents and your image captions if you include these in your writing.
This might sound silly, but it's important if you want to be taken seriously. When reviewing your writing check every piece of it.
Once done, you're ready for the next step of your writing journey.