Meeting aliens

In the movies and on TV all of the aliens we meet somehow speak English and look remarkably like us. If we ever meet an alien species things won't be this simple.

Will aliens even be able to breath the same air as us? Could we breath theirs? It seems unlikely that the air mixture of Earth is the only breathable one. It is possible that our air would be fatal to aliens, or theirs to us. Allergens and microbes in the air would further complicate this problem.

Would aliens be able to eat our food? It seems unlikely that aliens would be able to digest our food. It may in fact be deadly for them to even try. Some element common in our food may be poisonous to them.

Would we be able to communicate? We communicate mainly be vibrating the air but also with visual signals. Aliens might communicate with radio waves, generated light pulses, or chemical signals. They may not even use the linear pattern we use and instead communicate by using multiple channels at once.

Would we even recognize them as intelligent? If an alien landed a spaceship we would probably guess that it was intelligent. But if we landed on another planet would we even be able to recognize which creatures were intelligent and which weren't?

Meeting an alien species isn't as simple as they show on TV. I wonder how bad we will mess it up when we have the chance?