Paceline formats
The long, slow,double.
This pace line is used, as the name suggests, for long, slow and steady rides. This formation is good for easy 'social' rides. As you can see from the animation below you ride in pairs, taking turns up front. When the two riders up front have done their turn, could be one minute or 5 minutes at the front, they will split to the outside of the two lines and drift to the back.

Single Paceline.
This line is used at a slightly faster pace or where a long-slow paceline (above) is not practical. The rider stays on the front for as little as 10 seconds or up to 2 minutes - it all depends on how the rider feels. When the rider wants to go to the back they will pull off and 'soft pedal' until they reach the back of the line.

Single Paceline - side wind
This is the same as above but with a wind hitting the right side of the group. Because you want to position yourself in the slip stream this means you need to line up with the rider in front of you on your right - the upwind side. Now when the front rider changes to the back they will travel down the right side on the line - the up wind side.
The same this is true for a wind from the left, except the riders line up to the left and change down the left side, the opposite of the 'change right' animation below.

Double Paceline
This line is a very fast efficient line. This is essentially two lines - one going up and one going down. Except for a brief moment at the front of the lines you are always on a wheel, protected from the wind. In the example below watch the purple 'rider'. You can see that when purple is coming up the line he is on the wheel of yellow. Then when he is going down the line he is on the wheel of red. The only time he is pushing the wind is when he changes from the up line to the down line.
This pace line requires that the riders ride smoothly and pay attention (all pacelines do - this one especially so). When changing from the up line to the down line you must make sure you have cleared the front wheel of the rider at the head of the down line.
Two examples here are a wind from the left and from the right.


The rest is from personal knowledge and from other bicycling clubs/teams. If anyone would like to comment and/or Board Members want to change please do so.
Paceline Riding
The primary purpose of riding in pacelines to allow a group of cyclists to go faster than they could by themselves, with less effort for a given speed. Pacelines are about aerodynamics, efficiency and cooperation, and the right combination of these factors will allow you to gobble up the miles at a rate that would be otherwise impossible. For this reason, they are useful in many aspects of the sport. Whether you're in a breakaway in a race, trying to pull a break back, shooting for a PR in a century or just rolling out the miles with your friends, pacelines are an essential and highly effective tool.
In competition, they're often the reason that non-sprinters win flat races, or sprinters win hilly ones. Racing pacelines are most often temporary coalitions of riders from opposing teams who would usually be protagonists to each other, but are cooperating for the good of the group at hand. Once the group's temporary goal is achieved, the coalition breaks down and new arrangements ensue. And of course there are times in races when you want to disrupt pacelines for tactical advantage, but that's for another subject; racing tactics. For now let's focus on paceline techniques, as they are a fundamental skill for every level of road racing from local crits to the Tour de France. Pacelines are not just for racers, though; any group of cyclists interested in covering a distance quicker and with less effort would do well to make use of pacelines, and most of the same techniques apply.
There are basically two types of pacelines. The single, where all the riders are in single file and each rider takes a turn at the front and then rotates around to the back; and the double, where there are two parallel lines of riders. Single pacelines are usually reserved for smaller groups and/or maximum speed over shorter distances. Double pacelines work best with larger groups and more open terrain. Doubles themselves can be separated into three types; mirror-image, circular and echelon. Mirror-image doubles are generally used at lower speeds (and on wide roads), and work like two mirror-image single lines, with the two central lines advancing in unison and riders peeling off and falling back on both sides. The most common form of double paceline is the circular one, which rotates in one direction and functions like smoothly meshing gears, with riders rotating from one line to the other as they reach either end. The echelon is a variation of the circular that's used in strong crosswind situations, especially in racing. Like the mirror-image, echelons take up a lot of road and are thus impractical in most non-closed-road situations. Below are graphic examples of the different types of formations, with the three on the right being variations of the double paceline.

SOME GUIDELINES
1. The lead cyclist must observe the road far in front in order to decide far in advance the best route. If necessary to avoid a hole, sand or an obstacle, he or she must leave gradually the edge of the road and point to the danger to be avoided.
2. The lead cyclist indicates far in advance the traffic lights, the mandatory stops or any changes of road. If necessary to take an unprotected left turn, he or she must make sure that all cyclists have sufficient time to cross to the opposite lane safely; if not, he or she orders the group to stop and wait.
3. The lead cyclist should maintain a constant speed/effort and spin continuously. He or she must make no abrupt change in speed. He or she must not drink or eat while making the “pull” (being at the front)
4. The lead cyclist signals (hand down palm facing back) slows down before crossing a bridge with a longitudinally laid wood apron. The cyclists cross the bridge diagonally to prevent that their wheels fall suddenly in a slit between two boards.
5. The lead cyclist signals (hand down palm back with a side to side motion) and slows down before crossing a railway; the cyclists cross the rails perpendicularly. The group gathers before resuming cruising speed.
6. The lead cyclist make sure that the roadway is free of cars before dropping back.
7. When ready to drop back, the lead cyclist should indicate this to the cyclist directly behind him (elbow thrust outward). He or she accelerates slightly to move away forward, moves to the left (or right in double paceline), and moves down quickly to the tail of the group. The last rider in the line shall indicate by saying “last rider”.
8. In the peloton, the cyclists indicates holes or obstacles which are dangerous or likely to cause a flat. A cyclist who has no more energy to indicate the obstacles on the roadway becomes a danger to his companions. NOTE: We are a no drop ride group. Slow the group down and communicate the reason of your tiredness (bad choice of group, dehydration, bad food, etc). This is for the safety of the group as well as ensuring that you finish the ride. The group will still benefit from everyone staying together. Alternatives are to split into two groups (certified Ride Leaders available) and communicate the regroup point.
9. In the peloton, a cyclist who wishes to eat or drink should drop back slightly from the cyclist he is following, eat or drink quickly and carefully resume his original position.
10. When the lead cyclist is dropping back, other cyclists should make sure to move to the right as far as is safe in order to leave sufficient space so that the departing lead cyclist does not have to be too far from the edge of the road. In a double paceline, line(s) maintain the position and leaders drop to side.
11. In the peloton, one should NEVER overlap their front wheel with the back wheel of the cyclist in front of them. This is an extremely dangerous situation where a sudden move by the front cyclist will cause a serious accident for the cyclist behind.
12. The cyclist who stands up should shift up one gear then stand up smoothly in order to keep a constant speed and not throw his bicycle back into the front wheel of the following cyclist.
13. In descents, the lead cyclist pedals as hard as he or she can; the other cyclists keep their position. As the speed increases, an increasing gap between cyclists is necessary for safety.
14. In short uphills, the cyclists keep their position. In the longer hills, each cyclist goes up at his rate/rhythm, by taking care to prudently double by the left a slower cyclist. When passing, it is often good to say “on the left” so that the cyclist being overtaken knows you are there, and does not veer left into your path suddenly.
15. If overtaking a paceline, indicate verbally “On your left, right, middle (if double paceline).”
The essence of group riding is riding the paceline. It allows cyclists to travel faster with less effort and provides a better social experience. (It is also a foundation of racing.) Pacelines do have some inherent danger and require communication among the riders. But a good paceline is a wonderful thing.
More to come in the future.