First off, let me say I am not a member of the POV police, and do not support the idea a scene can only have one POV. However, I do want to stress that scenes with multiple POVs do require a clear writing style to work effectively.
First up, what do I mean by POV? Well, very simply, it is the angle from which the story is told. If your character addresses the reader directly (e.g. I went to the shops), this is 1st Person POV. If the author is the one telling the story (e.g She went to the shops) this is 3rd Person POV.
It is generally considered harder to sustain long works in 1st Person since you only have a limited view point in which to tell the story. One way around this is to have first person POV from several characters so the reader can see the other side of what is happening in the tale. In this case, I would recommend not switching POV within a scene, however, as it can become difficult for the reader to know who is currently speaking to them.
Third person POV can also be told from multiple viewpoints, and in this case it is possible to tell all POVs within a scene, so long as it is always clear who is speaking when you switch from one character's POV to another.
You can even mix the two. In my novella Hell to Pay, I have two characters in first person and one in third person, but I only swap between them by chapter to keep it clear to the reader whose POV they are in each time.
Here are what I consider the be the golden rules of good writing for POV:
1) Establish the Voice
Establish with the reader whose POV you are in, and make any switches between POVs in a way that is clear. The reader should never have to stop and ask 'Wait, who's head am I in now?'
2) Know the Limits
Make sure you do not imbue your characters with knowledge they cannot possibly have. If you are writing in first person (or in limited third person), the character whose head you are in cannot possibly know the thoughts going through the head of one of the other characters (unless they are clairvoyant of course)
Join me next month for my final How I Write post when I will look at plotting and pacing.