If you are sensitive to it, and if the group you are with is an experienced one, you can feel the energy coursing back and forth. It is always easier to run the initial 7 to 10 miles with one or more other runners than it is alone, especially if headwinds prevail. However, there is a tendency when running in a group to allow the group to dictate your pace, seemingly relieving you of the responsibility of staying on top of your planned race. But you need to continue to monitor your own pace at each mile marker. If the group begins dropping behind or getting ahead of your planned pace, gradually leave them and get into your own groove.
Some groups converse as they roll along.
Don't join in. Save your breath for later in the race. If someone addresses a question specifically to you, answer as simply and precisely as possible. Begin taking fluids from the very first aid station onward. When you approach aid stations, slow down, take your fluids, and walk briskly through the station area as you drink.