"When in Rome, do as the Romans do" is a funny cliché, but one steeped in truth.  Bulky ski clothes, heavy awkward equipment and clunky, slippery ski boots don't always make a vacationer feel suave, but there are ways to fit in and feel more "in the know".  Here are some tips for your best Ski Etiquette:

1. The number one offense:  When you carry your skis on your shoulder, DO NOT turn around quickly!  Skis are heavy weapons that extend from your back when carried.  Don't make people duck, and don't risk breaking someone's nose.  Either turn around slowly, looking over your shoulder, or put your skis down.  I've seen more "swing around" injuries than any other in the sport. 
2. Share your table at the lodge and cafeteria style restaurant.  Skiing is social.  Skiing is safe.  If someone can afford a ski vacation at the ritzier resorts, they are not there to mug you.  Invite others, you never know who you might meet, and there are great stories of how skiers met their future spouses, famous people or new ski buddies just from being friendly at the table.
3. Shake/stomp the snow off of your body and boots outside!  No one likes a cold snow or ice ball flung off of somebody landing in their chili.  No one likes those puddles of dirty melted snow on the tables, chairs, floor-yuck.  And by the way, to avoid losing things or ruining them when something at the table spills, put your hat/mittens, etc in the sleeve of your coat, and hang your coat up.  Only spread your gear out across the portion of the table you're saving to use when you leave to get your food, otherwise, keep it off of the eating surface.
4. Chairlift nose.  You're outside, you probably can't feel the drip forming on the tip of your nose.  It's a fact of life, it's natural, and it's gross.  Bring a tissue, and dab inconspicuously. 
5. Throw away your trash!  Yes, there are people for that.  But there are a lot more of you than there are of them, and before they can get to your junk, someone else on vacation (i.e. not getting paid to be your mom) might have to deal with it. 
6. Know which services/people customarily receive gratuities.  This is frequently different at ski resorts than other vacation locations.  Of course, tipping is always at your discretion, but if you don't want to feel like scrooge when someone does something really special for you, and you decide to reward them, get the 411 ahead of time about what is standard. 
7. Ask before lowering the safety bar.  And always lower the safety bar.  It doesn't look stupid, it looks like you know what you're doing (or at least like you've skied enough to have seen what can happen when it's not down).  Be aware, though, that the guy on the end of the chair might not be ready, and pinched elbows and dropped ski poles don't make for a friendly ride up.  Be sure to say something before you lift it at the top, too.
8. Know those skier safety rules.  They are nationally consistent (and sometimes state law), common sense, and (duh) for your safety.   Also be aware that things do happen, and just like driving, extenuating circumstances sometimes prevail.  For example: the rule that the person in front has the right of way....doesn't always happen.  Don't force the issue, just take the safest alternative.  This is why you wear a helmet. 
9. Don't teach family.  I don't even do it.  The dynamic is almost always too weird.  Not to say that it is always a disaster, just that there is very little at risk for handing over your loved one(s) to a professional and freeing yourself up to enjoy the main reason you are here....to ski.  Otherwise be prepared to be entertainment for the locals.
10. Smile.  You are on vacation.  You are not riding the subway!  It goes a long way, and it makes you feel good, too!

EXTRA CREDIT:  This is the one all locals want you to know:  Do not ski to the entrance of the lift line, stop, then look around for your buddies while blocking the line!  Pull far to the side of the "maze" and make sure your group is ready before you get in line.  Take care of equipment/bathroom/ski pass fumbling BEFORE you get near the start of the lift line ropes!  And please pull over to the side when you disembark the lift, too, so that others may ski through....You don't even want to know what disgruntled skiers will do on a powder day to lift line blockers!