Anticipate without sudden movements
You ride differently in a group compared to riding on your own. If you ride on your own, and there is a puddle or a pot hole on your path, you steer around it. If the road is narrow and you need to make room for an oncoming vehicle, you can quickly move to the side.
If you made these movements just as quickly in a group, there is a fair chance that someone behind you will be surprised. In the worst case, withe a crash as a result. In any case, it makes riding in a group erratic.
Look ahead and change slowly
The trick is to look well ahead of you for changes in direction or speed and then execute these changes slowly.
On the open waters, there are differences between large and small boats as to how quickly they can change direction or speed.
As a cyclist, you are on your own more like a speedboat, as a group more like an oil tanker.
In a group, you’ll find yourself riding through rather than around puddles a whole lot more than on your own. Because you don’t want to make it too dangerously for the ones behind you. It’s better to be a bit wet then to be a liability.
Most often, changes in direction are also notified by signaling.
See also Signals
In a group you take much more time for stopping than when riding alone. Of course you signal that you’re stopping.
If you anticipate possible changes, you then have time to change slowly and you will find that the group will maneuver around various obstacles much more fluently. The speed remains higher and you have fewer problems with the ‘accordion’ effect. Also, there’s a lot less screaming and shouting, and your group will ride in a nice kind of flow.
If you’re at the rear of the group, it is easier to anticipate on what’s going to happen by looking forward through the group. Just looking at the rear wheel of the rider in front of you is literally being shortsighted :).