If you read books or web sites on fiction writing, it is not long before you encounter "the rules":

Don't use adverbs.
Don't use passive voice.
Don't change point of view within a scene.
Show, don't tell.
Don't "infodump" background information.
Use short, direct sentences.
Begin the story at the point where the plot takes off.

(...and there are more, of course...)

The interesting thing about these is that they are not actually rules. Unlike conventions of spelling and grammar, breaking them does not make you seem illiterate. Rather, these are style suggestions. Open a published novel or short story; it won't be long until you come across a violation of these rules. Furthermore, these represent the current fashion in the US (and, to varying degrees, other English-speaking countries). Go back a century or two (or even a few decades, in some cases), and you will encounter very different stylistic fashions.

Nevertheless, aspiring writers concern themselves a lot with these rules. I think there is a hope that adhering to them is the secret key to getting published, or perhaps rather a fear that violating them means a quick toss into the rejection bin. It's possible to get swept up into a state of stylistic paranoia, which makes it that much more difficult to find your own voice as a writer.

So should we forget about the rules? No. They represent a distillation of experience in where novice writers go wrong. They are important correctives, able to turn really bad writing into competent (if not necessarily great) prose. Like many rules, they can be broken, but it's best to learn them first. Violate them when you have a good reason to, not out of ignorance or sloppiness.

I found Ursula K. Le Guin's Steering the Craft (see my review here) to be helpful in keeping "the rules" in perspective. Rather than treating them as sacred writ, she examines each stylistic question from several sides, often arriving at a fresh perspective in the process.

Here's how it all settles out for me.

I don't worry about the "rules" overly much when writing. It just slows me down. When I edit and revise, however, I pay attention to them. Violations become flags that raise questions: Is this adverb necessary? Would an active sentence work better here? Is this bit of exposition too long or too boring? I often end up making changes, but not always. (I have sometimes adhered very closely to the rules, to break down some of my own stylistic habits. That's a worthwhile exercise.)

I also make regular "reality checks". I notice stylistic matters when reading good published fiction. How often do my favorite writers use passive voice? Adverbs? Complex sentences? If my own writing falls more or less in line with the practices of good writers, I'm not going to worry about these things. Better to focus on other aspects of the art and craft.