Keep in control at all times. There's no excuse for losing control and running into another rider or fixed object. You risk injury to yourself, those around you and your equipment. Keep in control, fall down if you have to and maintain a safe speed.
Right of Way
Skiers and riders in front of you have the right of way. This is pretty intuitive since you're looking at them, but they have no idea what you're doing behind them. Since you can clearly see them, it's your responsibility to navigate safely around. This doesn't mean cutting them off by inches, but allowing a safe distance to pass.
Though riders in front have the right of way, there's no way to provide right of way unless they're visible. Therefore, you need to stop in a place that is visible to others and doesn't block their path. Stop to the side of the trail. Be sure that there are no blind curves or hilltops preceding your stopping point. You should have a clear view up the majority of the slope to ensure that those coming down have a clear view of you.
After taking a break, it's always tempting to just jump up onto your snowboard and proceed down the slope. Before you hit the green light, you need to safely merge. This isn't usually a big deal since a ski slope doesn't look like a highway at rush hour (usually). However, it's still important to look up the hill before you start riding down. Also, be sure to safely yield to other riders when encountering merging slopes.
Ski resorts employ signs to provide important safety information and instructions. Riders should always be alert and observe signs. Some important signs include "Closed Trail," "Slow Area" and "Merge." Paying attention to these signs helps keep you safe. Additionally, follow the out-of-bounds policy of the resort and don't ride in any prohibited areas.
Use leashes to prevent your board from falling from the lift or sliding down the slope. While this rule is in need of an update, since leashes aren't as stiff a requirement as they used to be (for good reason), it's still part of the responsibility code and should be considered. If anything, check with the individual resort as to their leash policy.
Lifts are one of the most intimidating parts of snowboarding for beginners. While one may not be a lift pro right away, one needs to understand how to safely load and unload a lift. This will be mastered with practice, but the basic method can be learned by talking to others, watching those ahead of you or taking a lesson. Taking a lesson is a good idea for the first time anyway.