Jane Friedman has answered some typical questions about who and when to have people read your manuscript before publishing.

I always encourage a writer, before they hand a manuscript off to anyone, to print out the piece on paper (or look at it on a different device e.g. a tablet vs a computer screen – it’s not quite a good as looking at it on paper but it does help make it appear different to your brain). Once you’ve got it on paper, read it out loud. These two things can greatly help you self-edit before you ask others to take their time to read your piece.

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Developmental editors, critique partners, sensitivity readers, friends—feedback comes from different people, for different reasons, at different times.

Source: Peer Critique Versus Professional Editing: When, Why and How to Use Both | Jane Friedman