Talk to him first about what you will be doing, there is a big difference in comprehension level between an infant and a two year old. If he knows what to expect it will relieve anxiety.
Make sure he has run around enough prior to getting on the plane that he won't be dealing with pent up energy. Be sure to have plenty of books, snacks, toys, etc.
The last and most important part is up to you alone. Plan for it to be a fun adventure, a new experience that you are giving him. Be aware of, but nor over sensitive to the passengers around you and don't let some suit who doesn't know about children ruin your trip.
