Clarity is king in my - forgive the pun - book. And one of the things that I find time and again when reading drafts is that people forget the reader is a book reader and not a mind reader - in other words the author assumes the reader knows what the author is thinking.
This stretches into pronoun usage in many cases - the author knows what they mean by "he" but it can be confusing to the reader. Take this example where two characters of the same sex are in a room at the same time (let's call them Ed and Fred)
Ed walked into the room and glowered at Fred. He looked at him for a long time until he couldn't take it any more and punched him in the face.
Now with a bit of work, you might work out who is doing what to who, but unless you're a mind reader you can't be one hundred percent which he the author means at all times.
Ed walked into the room and glowered at Fred. He glowered at the other man for a long time. Finally, Ed couldn't take it any more and punched Fred in the face.
The pronoun usually refers to the last person or object mentioned - unless it is perfectly clear that it doesn't (in the example above the first "he" clearly refers to Ed rather than Fred if we're in Ed's POV). But where it isn't clear you should be specific about who you are referring to. Sometimes this means you might have to change your sentence structure as in the example above.
But what's important is clarity. If you confuse your reader too often with unclear pronouns, chances are they're going to put your book down and go take an aspirin for the the headache.... before picking up another book which might be clearer and more comprehensible.