On to Journeyman-level POV/Tense Discussion
One thing I'll occasionally do is split a scene between POVs, which is another one that's against Robert's Rules (so to speak)-- mostly to develop different characters internally. On redraft, I often go through and take a number of those out. On the other hand, I find that characters often look very different through different eyes, and it's a fun way to build three-dimensionality. I'm trying for a John-Brunneresque kaliedoscopic effect with my current WIP, where the reader knows much more than any of the characters, and as it moves into the second half and the characters are starting to put the pieces together I'm finding fewer POVs are necessary.
Here's the thing: it drives some readers crazy, because it's not the measured way they're accustomed to being told a story--in a linear fashion, with long segments in each character's POV moving each character through a story arc. I'm choosing to do something more like showing the significant flashes of each one's existence, and only really deeply exploring the arc/story from one character's perspective. Everybody else gets a few licks in--it's an interesting experiment. But I've come to the conclusion lately that taking risks, once you're more or less confident in your base skills, is a Good Thing.
And being aware of the tradeoffs of various POVs is also a good thing. If you choose first person or tight third single narrator, you'll be able to show less of the story and risk having to play games to show readers things--or just out and out tell them. (I got complaints in my first novel from a few readers because I didn't show a fight scene my first-POV narrator wasn't there for... including some truly wacky ideas for how I could have shown it... like having my narrator develop psychic powers. :-) )
But when you choose a POV, you accept those tradeoffs. I'm not going to be able to do deep characterization of all the POV characters in my current WiP. There are going to be things that seem arbitrary or abrupt in most first-POV narratives, because there is less opportunity for setup and so forth than there is in third POV--unless you play the kind of egregious tricks Robert Sawyer does in CALCULATING GOD.
I'm a big fan of POV tricks, as anybody who has read my stuff probably knows. But I will say that I didn't start pulling them hardcore until I was very confident in my ability to tell a story in plain first person and in plain third person. I apply the Picasso rule: save the stylistic insanity until you have explored to some extent the limits of what you can do with more standard techniques. They're more flexible than you might think, and there's no point in being stylistic just for the sake of being stylistic.
Picasso could *draw.* A lot of his imitators--cannot. And it shows.
So taking risks is good. Trying to run before you can walk well, well--it's just going to slow you down in the long run, because you'll have to go back and learn how to do it eventually.
When you start playing with tense, you start playing with reader expectations: I'm very comfortable in first-POV present tense, but I use it rarely (four places, so far--although two of them are for a single POV in multipov novel-length works) because it can be annoying and it's easy to overwrite/drive your reader crazy with it.
For me, it doesn't create the sense of immediacy that many people seem to be aiming for with it, but rather a sense of frozen time. So I use it for that, and for alien/animal perspectives, and in one case because my damned protag loses her charm when I put her in past tense (weirdest thing ever, but no kidding, it's true).
Anyway, a lot of rambling there. But it seems to me that the most useful technique is the simplest technique that will serve a story--elegance, in other words, of construction--and that the fancy stylistic flips and folderols will be the more effective if you use them when you *need* them.
Instead of any time you can find an excuse.