You have the greatest opportunity to impact the players. If something is going on with the defense, you have the period between downs to talk with players. If it's a blowout, you can keep players' heads in the game. Can't tell you how many volatile playoff games I've been involved in where I had an opportunity to talk to the team that was winning and remind them that they needed to keep their cool, since they would be playing next week.
Don't walk off penalties yard by yard. For example, walk the first yard, jog the next 8 yards and step the final yard for a 10 yarder. Looks more professional than taking 10 steps.
Yes, they teach you to stand still when a runner is coming at you but it doesn't always work. If I know I'm in the way and I have time, I'll move toward the LOS away from where the hole appears to be. Be ready to use your forearms to "block" runners away from you if necessary.
In 8 seasons, I've only gone down one time and I've helped up more than my share of DBs who didn't see the wall (me) that they ran into.
BTW, linebackers are big and dumb and they will step on your feet. What makes it worse is they're usually pivoting when they do it. OUCH.