3 writing no-nos that are actually yesses

I've noticed that people tend to obsess over certain "rules" to writing that, frankly, don't make any sense. For example:

1. Do not use contractions. Nothing makes me laugh with more embarrassment than when someone writes, "Let us" instead of "Let's."

2. Do not write in the first person. Why would I want to read anything -- even a direction manual -- that sounds like a robot wrote it?

3. Never begin a sentence with a conjunction. It's called emphasis, people. Criticizing someone out for starting a sentence with a conjunction makes you look like that girl in Freshman English who peer-edited my paper. Forest for the trees and all that.

These "rules" remind me of how the Victorians wouldn't let their kids ride bicycles because they were afraid they might accidentally masturbate. RELAX!

What about some rules to help us eschew obfuscation? Shorter paragraphs, smaller words, fewer passive sentences...