If you're looking for real help on a completed manuscript, you most likely need someone with actual editing experience. This isn't to say that friend readers can't give useful input - but effective editing is a real professional skill and not everybody does it well. It can be especially hard for writers, since editing is not the same as re-writing, which - for writers - is always a temptation. Critique is not the same as fix. You don't need to know how another writer would write your book; you need to know what you should do to write it better.
A trusted reader is important and it's wonderful to have one - but a rule of thumb is that the trusted reader should not be a family member or a buddy unless (1) you can absolutely count on them to give you an honest and possibly unpalatable critique which (2) won't destroy your relationship forever, and (3) you have good intellectual reasons to respect their advice. Not all opinions are created equal.
The other thing to think about is that asking somebody to read/edit/comment upon a manuscript is a huge deal - it's a request for a major time commitment. At publishing companies, your editor is paid to do this (yes, they're PAID to make hateful comments). (Usual practice: they send one paragraph about how much they loved your book, followed by four single-spaced pages of everything that was wrong with it.)
Not-yet-published authors have the option to send their manuscripts to a professional editor - if you check online, there are manuscript editing services all over the place. These do, however, cost, and obviously that's an issue. But if you're serious about your book, might be worth the investment.
A good editor can make a huge difference.
Rebecca Rupp