Always have sources to hand when creating and expanding articles. Don't write articles based upon your own personal hypotheses and inferences. Don't write articles based upon knowledge that you half-remember learning, but have no idea from where or from whom. Write articles based upon actual, concrete, sources, and ensure that the article cites those sources. If you half-remember something, go and hunt up a source that covers it first, then write.If you don't do this, expect your articles to be speedy deleted, nominated for deletion or asking the AfC help desk why your article was declined.
Calculus is good for mathematicians, and it's good for Wikipedians too. Don't worry about how competent an editor is now - focus on the first derivative and worry about their rate of competence change. A good newbie can teach themselves to become more competent. A bad newbie never will.
In any debate about the merits of a musical act, be it solo or band, as discussion continues, the probability of comparing the perceived quality of the act to Justin Bieber approaches 1.
Every time you start a thread on WP:ANI, God kills a kitten.
My own wikocratic oath is : First, cause no drama'.'
I really wish wikilawyering were against policy.
"If I had a choice between trusting a compulsive liar locked in a straitjacket in a padded cell scrawling his inane ramblings about how the lizard people secretly run the world through an extensive mind control programme on the wall of said cell with his own faeces and trusting what is written in The Sun, I'd flip a coin because they truly are about equivalent in reliability."
"It's important to remember that however set-apart and distinct we feel the project is, the point of contact with the real world is the user of the encyclopedia, the person who pops into Wikipedia to find some needed information or just to browse a bit, and couldn't care less what the Wiki-world experience is like to those inside of it" 
If somebody tells you to "get a life", they might have a point. Enjoy editing Wikipedia, but don't let it consume you, and make sure you experience the real world enough to get perspective on things. Especially if you have a wife and kids.
When people have problems with editing wiki markup, it's a problem with the software's poor interface, not the end user.
If you see an angry rant on a talk page about your revert to that article that talks about "the truth" but ends with — Preceding unsigned comment added by..., you can probably ignore it. If it's an IP, you probably can rest safe that your revert hasn't even been touched.
There is no race to be "first" to answer a question on WP:HD, WP:RD, WP:AFCHD and WP:ANI .... all you get is an edit conflict with SineBot for your troubles if you're lucky.
If you want to be an admin, find your best friend's car, take out the rotor arm, slash the tyres, then tell them to their face you did it. If you can survive the abuse you get back, you might have what it takes.
Twinkle has a lot of magic buttons to automate tasks. None of them are for writing content and adding sources. The best content editors ignore twinkle, and vice versa.
Assume good faith can mean deleting an article or doing a blanket revert, then apologising to affected editors that you needed to do it.
Those that can, do. Those that can't, bicker about the manual of style or the citation guidelines. I mean, who cares that somebody's falsely accused of murder - just put that bloody full stop BEFORE the ref tag.
If I see one more editor throw the term WP:RS at a newbie without explaining what it stands for and why it's relevant, I will scream.
One of the most dangerous habits you can get into is to take Wikipedia too seriously. Dozens of editors have been indefinitely blocked at ANI and Arbcom because the encyclopedia is super-duper important and blocking them is soooooo unfair.
If you think one of my edits makes the encyclopedia worse, revert it. Please try and leave a good edit summary or discuss it on the talk page, though. In return, I pledge I will only revert your changes once and once only, if at all. If you revert back again, then I'll go to the talk page. Or I might decide you're correct. Either way, I have no more right to edit this place than you.
^Reliable sources are many and varied but are generally not : Facebook, YouTube, Twitter, Soundcloud, blogs (that aren't written by notable journalists for the New York Times or something of that level) and the website you created yesterday