I'm editing one of my old unpublished books for e-book, and it's interesting to discover lots of craft points that I now bring up with writers starting out. Most obvious of these is viewpoint again.
First off, there are too many extra viewpoints (though I will have to hang on to a couple as I don't want to wholly rewrite the story). Second, there is head-hopping like mad. Third, the viewpoint when there is not polished.
A common mistake on the latter: characters allegedly in viewpoint are spoken of as if someone else is talking - eg "a reminiscent smile rose to his lips". No! He can't see himself smile. He can only feel the reminiscence, and if he smiles, he smiles. It's in viewpoint, it has to be active. We are not in the smile's viewpoint!
In essence, this type of writing is authorial. In other words, it's author intrusion - telling the reader, which makes it passive, rather than showing it in the character's head/heart, which is active. The result is to distance the reader from the character. Head-hopping has the same effect because the reader has to switch identity from one character to the other. This is why most writing advice suggests keeping one scene to one character's viewpoint.
I'm not going to be able to iron out all these errors, but I'm doing as much as I can without getting into major rewrites on the story. What's good about it is that all these years down the line I've learned the craft so well I can spot this stuff easily. And it isn't as if I've "studied" it. I've just written and written and written.
So don't be dismayed if you are only on your third, fourth or even tenth book, and you still find you're making this sort of mistake. (This particular book was in fact my 12th full length novel!) You are learning and you will get to the point where you can do it fully in viewpoint almost without thinking. And your writing will get better and better because you will pull your reader into the story and hold them there.