You've got to start somewhere.  Don't treat the newbie on the field like he's got some kind of disease!  Help him out, answer his questions, tell him the real deal about paintball and how to play.  You never know, the newbie next to you could be the next Bob Long.  If you meet someone on the field and it's their first time.....
1) Treat the new player with the respect that you would any other player, nothing would make them feel more comfortable about paintball than if that one person was nice to them.
2) Make sure that they understand the safety requirements, because nothing is worse than a blind newbie (or a newbie blinding anyone else for that matter). 
3) Help them out with their paintball gun.  If their barrel comes off, don't tell them that they should make a suicide run because their gun is broken, help them out a bit.
4) Squeegie their paintball gun barrel if they need it.  Don't forget that a new player can eliminate any player, and a straight ball or a curved ball could mean the difference between winning a match or losing one. 
5) Answer their questions? TRUTHFULLY.  If they ask you if a paintball hurts, don't tell the story about how Uncle Bob got hit in the ribcage with a paintball and nearly died, just say it only stings for a few seconds.
6) Explain things to them in a way they would understand. "Yeah, I got an RVA on my P68SC and I think that I might rig her up with some HPA after I buy my KP2?" WHAT!?!?!? Don't expect a new player to understand that kind of talk.  Remember, they might not even know what a Stingray is, or what a burst mode is.
7) Help them on the field.  If they are in the same bunker as you and they say they want to go some other bunker, provide them with some cover fire. Don't just shove them out of the bunker and take their spot.
8) Give them advice.  If they ask you to give them cover-fire to what you know is a death trap, then don't just play along, tell them that another place is better, just try and prevent them from getting themselves eliminated.