Though everything in the Guides is important, here are the overarching things that are the most vital.
Everything in the Guides is Important. Each required guide has been carefully reviewed and edited by Staff members to ensure clarity and brevity. Small things that are in there really are important, and I don't think I can stress that enough. This guide is here to go back over the most basic and important things, but everything matters.
We are a community… We're a creative writing site, not a corporation. Nobody has any obligation to read, critique, or vote on anything. We're also mostly college-aged or older here, and for those of us who aren't, we try to act like it. This site is something we do for fun and nothing more. Acting like an immature brat won't win you any favors.
—on the Internet… Normal Internet etiquette applies here. Not necroposting, acting mature, and respecting the staff (know who they are) are just as important here as they are on any forum or creative writing site. Utilize the chat. Also, we want you to take the site seriously if you plan on staying, but nothing here is life or death. It's the Internet; relax a little.
—full of assholes. Yep. We have extremely high standards here. No matter how good a writer or person you think you are, it's different here. Taking your time with writing and getting help in #site19 or the forums is the best way to go. We'd rather have good material than a piece of shit: period. Though the community can come off as brusque and mean at first, if you're polite, patient, and mature, we open up rather quickly.
You are not the next "thing." Nobody should expect to make the next group of interest, finally kill 682, or create the next best agent. Don't join expecting to make a huge splash. Most importantly, don't expect yourself to be superior to anyone. We generally tell people to shy away from Keter, Joke, and Humanoid SCPs for their first attempt because they're really, really hard to pull off. Anything that difficult to execute, or more difficult, should never be attempted on a first try. If you think you have a great idea to make your mark on the site, don't do it first. Please don't take this as a challenge. If you want a challenge, try to pull off 'next big thing' after you've got a few successes under your belt. Few people can pull this off either, but trying won't annoy as many of us. Maybe.
There is no single way to write. There are many different schools of thought on how to write an SCP (or tale), all of which can work. For this reason, some advice may be contradictory. In general, you can tell from a user's profile and/or authorship how good their advice is. Keep in mind that it's still your SCP though, so go with whatever idea you like best and think can work. If multiple people tell you an SCP is going to fail, it is going to fail.
Reading's really important. Read everything you can. No one will ask you to read the thousands of pages on the site, but the best way to get the grasp of site culture, tone, and other things is to read a lot. If you can't stand reading tons of pages, this site isn't for you. Also, read all the guides, because everything in them is important and if you can't manage to read six pages there's no way you're gonna last here.
Beyond this, I have decided to compress this guide into a short sentence, that you should remember during your time with us: Don't be an annoying dumbass, and read all the guides.