Welcome.
The FAQ is a great source of basic information even though it's probably a year behind now; most of the info is still accurate. Most items come with readmes but only half of the readmes I see actually have useful information.
Ask questions, even if you think they've been asked before - don't bump month-old (or older) question threads to say thanks but do make a new thread if you need more information or ask in the general SMW hacking help thread if you believe the answer might not be so complex or if you're going to be asking numerous questions in a short period of time... it's just an observation of mine that people tend to get flustered when a user makes dozens of help threads in a short period of time.
Criticism on your work is worthy of consideration, but apply it if you feel it will improve your work without changing what it's about. You don't want to compromise your project's goals, and don't try to please every player because it's not possible.
Reality Corner is zero-tolerance for low content posts, so try not to be silly there. Being silly elsewhere is fine but try to keep it relevant and thoughtful too since there's been a strong crackdown on garbage posting lately.
Hack moderation is not a substitute for beta testing - it's assumed when you submit a hack, you're sure you've fixed as much as you could have and this is what you want to be seen. Keep in mind that you want to submit content to the SMW Hacks section linked to in the menu and not the Temporary Hacks section on the main page. (Temporary hacks aren't temporary: the section is just temporary until all the hacks are reevaluated and then it will be merged into SMW hacks.) You DO want to use either AddMusicK on your hack or ensure that all your songs have valid echo delay settings so the game does not halt in accurate emulators or on real hardware. I am currently enforcing a "no broken hacks" policy so even though you may have ZSNES as your favorite playing emulator, higan/bsnes or at least SNES9x testing is a must for a final submission - the exception is the "broken" legacy/Temporary hacks which are being grandfathered in because they were originally accepted before the remoderation.
IRC is fine if you want to get social with people quicker but you will be exposed to the more shameless side of SMWC society. Some people will desensitize you to crude humor and challenge your views, which may be a good thing in the long run, but inversely, they may annoy the hell out of you. Try to avoid tight cliques that hate other tight cliques. Whatever the case, if people annoy you, don't try and change them, but if you are being harassed within an official channel or query messages, report it to staff. Be aware that some people will say NSFW things and if you're not okay with that or your parents aren't, use the /ignore feature. The forum is generally more clear and serious but it's also much slower.
If you're maximum ricer, a post layout request thread exists in Computers and Technology or you can learn to make your own through CSS and HTML tutorials. It's (just like) web design, but you have to make sure your changes are only in your post box and that they don't override anyone else's or any other part of the site. You don't really need layouts and avatars, but keeping a consistent one helps users easily remember you and how you are around these parts.
Just look above you...
If it's something that can be stopped, then just try to stop it!