So this is a very situational question and is very dependent on the amount of resources that you have.
As for me, I would recommend that you proofread it by yourself once, so you would ask for outside proofreading help after the second draft. In the earlier stages, you want more constructional feedback (like examining plotholes or looking at character errors) that effect the basis of the story, while during later stages, you want more editing help, such as making minor changes or correcting grammar errors.
Obviously, you can ask for quite a bit of proofreading if you have the monetary resources or a lot of willing friends, but otherwise, I would stick to proofreading it once by yourself, and then asking for outside help.
I hope I was at least a bit helpful, I can only provide as much help as my experiences give.