For the love of bunnies, cover anyone building/welding/carrying a GL. These people rely on you to cover them, not to bhop around aimlessly while throwing your guns in the air.
Not I! I am proudly self-sufficient with my GL, though if you're nearby, I can't vouch for your safety.
However, sometimes it's nice to see a skulk rush fail miserably with a well-placed grenade into the lead skulk, so I'm not -too- bad to have around...though I bet most would prefer me not to have weapons that kill them too.
But as another general rule that I think everyone should list:
BE AWARE OF WHAT'S GOING ON.
Check your map every now and then if it seems a little too quiet, look around, patrol, things are never supposed to be quiet, and things are never supposed to be simple. Find something to do if you have nothing.
In response to meatshields. A few words for you all:
FOR THE GOOD OF THE MANY!!!
If others are better shooters, it's your turn through that infested doorway. If nobody else goes, what good does standing around do? It only takes one marine, and you do respawn. Suck up your pride and take the steps. That, or push MrBill through.