Noun or Pronoun

QUESTION: When should I use the character's name and when should I use the personal pronouns "he" or "she?"

Name repetition reminds the reader that he is reading about a character, and it jerks him right out of that viewpoint character's head. For this reason, you should use the character's name once at the beginning of the scene, then you don't use it again except for clarity.

Moments when it's needed for clarity include scenes with more than one person of the same gender. 

In crowd scenes, I've always found that it's better to be a bit boring using the character's name, which the reader will skim, than to confuse the reader as to who is doing what action. This stops the reading process completely which is the one thing a writer should avoid at all costs.

As in real life, you shouldn't overuse characters' names to address each other in dialogue, either. 

Names are most often used at the beginning of a conversation as people greet each other. "Hello, Mary, how are you?" 

Or they're used to impart important or emotional information. "He's dead, Jim."

Or to direct conversation at one person in a group of people. "What's your opinion about this, Fred?"