We generally ride in a stagger formation for safety reasons. The minimum recommended spacing to the bike directly in front of you should not be less than two seconds (the two second rule). The bike in the lane to your left or right should not be less than one second ahead of you. You will find that two seconds is a long distance when riding at highway speeds. That is it's a long distance when everything is going well. When things go wrong, however, two seconds distance is gone in the time it takes to figure out you are in trouble. Remember, this is only a guideline. You certainly do not want to ride any closer than these intervals, but if you are more comfortable easing back a bit, than by all means do so.
The two second rule is only a rule of thumb. We should try to adhere to this rule when possible, especially at highway speeds. There are times, however when it is best to squeeze together while in city streets & while slowing for a stop. This will help prevent cars from entering the group.
The last bike should ride in the middle of the two bike lanes with all head lights and running lights on. This will help the lead bike see the last bike. Refer to the image to the right.