I've been travelling in a group of 5 friends over the last few days, and here is a few things I have learnt. Obviously, being cautious even in a group, should go without saying, but there are certain benefits.
Solo players are incredibly scared of you, and the further you are inland, the more they will avoid 3 or 4 grouped players.
On the coast, the freshly spawned survivors are a little more reckless. Do not ever go near the coast.
Stick close together, close enough so that if someone sees you, they see all of you, but not so close that they can gun you all down. Once again, solo players who are inland are usually better equipped and will NOT
take that chance to try and kill 3 players.
You have to move as a group, at all times, maybe 10-15 metres max
between you all. Always try to know where your group members are, alt+mouse movement is a wonderful thing. Remember, if one of you appear to the outside observer as being alone, chances are, you will be shot!
Call shots. This serves two purposes... one, you will not be scared shirtless when someone starts firing. Two, if none of you has called the shot. You will know there is another survivor nearby.
Zombies. It is imperative, that, if someone comes under attack by a zombie, that they try and stop moving as soon as possible, when you are in a group, a zombie will not kill you, even a horde will have trouble (although if the horde has awoken, its best to not shoot, and just run for the nearest building/chokepoint). If a zombie is attacking a party member, them not moving and taking a few hits is much better than moving into someone elses line of fire that may be trying to save you. Stand your ground, stay calm, and do not move.
I will not take a shot at a zombie that is attacking a friendly player, if that player is moving.
Lastly, raiding inland villages...We are going to try out this tactic, but in theory, it seems sound so far. This should work with five players ideally, but can work with four. With five of you, station two players (distance them a little for vantage) in the hills/forests around the village, trying to avoid likely entry spots. These guys are to be your eyes for bandits/survivors who may try entering the village. The other three enter the village. You need at least
three players to raid safely, as three players versus the horde, or encountering a solo survivor/bandit are more than intimidating.
The three inside the village, can then gather loot for everyone (there may need to be a shopping list of some description) so making sure you have enough bag space is also a good idea. While the two outside keep watch. If they see someone, its up to you whats next, my approach would be to /sidechat them without giving away the town "You running across the field towards x building stop, this is a warning shot" and get one of your watchmen to fire the warning shot. Then I would explain to them what is happening. I guess after that, if they still insist on entering the town, it would have to be weapons free, because they are no longer coming in for a chat and a cup of tea..
Finally. Bandages. Always know how many bandages you have as an entire group, and who has how many. Always.
p.s Bandages. at least 3 or 4 per player... at least. Other medicine such as painkillers is handy. But Bandages.
Sorry for the rant.. hope it was helpful!