Since we do, and should, practice group riding (whether in smaller or larger groups), here are some things to think about:

1. Consistent speed is very important. There's a huge accordion effect when someone in the front speeds up or slows down. Check your speedometer while you're in the pack, and when it's your turn to pull, maintain that same speed if at all possible. If you CAN'T go that fast - you shouldn't pull, just rotate smoothly off. If you want to go faster, consider the needs of the group - and if you think it's a good idea to increase the speed a little, do it very slowly, and only after you've been at the front for about 30-45 seconds at the same speed - then you can increase the speed by about .5 - 1 mph over the course of one or two minutes - SLOW and SMOOTH - no surges.
2. Don't touch your brakes. There is no good reason short of a traffic stop, crash or impending crash to touch your brakes while riding in a paceline. If you need to bleed off some speed, sit up a little higher, or pull over out of the draft a bit. Again, braking causes a huge accordion affect and can be very dangerous. If you do need to slow down for a turn or stop sign, do it well in advance, and loudly announce your intentions verbally and with hand signals.
3. Point out hazards. In a proper paceline, you can't see around the person in front of you. It's your job to let the people behind you know if there are road hazards - point them out - verbally and with your hands.
4. Check for traffic when you're rotating off - this is really important, and often overlooked. If you're about to rotate off, make sure there are no oncoming cars.
5. Only use a double paceline when traffic allows - on empty backcountry roads, it's probably OK, but use good judgment. A single paceline is easier, and is usually more appropriate for the type of riding we do, especially in smaller groups, which, as I said above, is better anyway.
6. Maintain a proper distance. This one is a bit of a judgment call, and what is proper for you might not be proper for everyone else. 6-12" is probably about right, but only if you're comfortable with that. If you're not, go out and practice with other riders and get more comfortable at that distance.
7. AS TRAFFIC ALLOWS, adjust your position according to wind direction. See the website below for more details...
8. Be predictable - hold your line, no sudden movements, etc. If you can't ride in a perfectly straight line whether you're just riding, taking a drink, stretching your neck or scratching your ass, practice until you can (note: this isn't easy, and most people WILL need to practice this - ride along the white line, staying right on it for a mile or two, then do it while drinking, getting into and out of your aero bars, etc., repeat until you can stay within an inch or two of the line)
9. Protect your front wheel. This is related to some of the items above - but it's an easy way to think about what you need to be doing in the paceline - try to avoid positioning yourself in such a way so that someone can swerve into your front wheel, which is likely to cause you to lose control. In other words, avoid overlapping your wheel with the person in front of you.

And remember - it's OK to get out of the paceline if you feel uncomfortable due to your abilities or someone else's - triathlon is a solo sport, so you don't NEED to ride in a paceline.

Thanks for reading - ride safe and have fun!

There are some good tips and diagrams here.