Just give him plenty of rest and sleep. The different viruses that cause common cold have their incubation period, after that the symptoms such as runny nose and cough will slowly go away. Most doctors will not recommend any medication unless there are symptoms that point to infections, so avoid taking antibiotics and over the counter cold medicines. A person suffering from cold usually feels fatigued and tires easily, so let him stay in bed longer and if necessary, let him skip school for a day or two.