My guess is they would be so strange that communications would be close to impossible. However, it is pretty safe to say that any plausible scenario for our meeting would presuppose a curiosity about the natural world similar to ours, and that is a basis for communication. The following remarks are based on the premise they find us, so they are a spacefaring species, or at least have the technology for interstellar communication.

They would be interested in our biological sciences, since we have had much longer to study them than they, but I doubt our physics, chemistry and engineering would be very useful to them. Theirs, would be very interesting to us. We would be interested in each other's sociology and psychology, and if they had any, their philosophy (my own prejudice is that, like art, religion and sport, philosophy is a strictly human activity). Mathematics is probably the only area where we might have an advantage over them (clearly, we know much more math than our technology seems to require, they might be just the opposite).

But there is a very strong possibility that they may just not care about us one way or the other. They may not be hostile, but that doesn't mean they are friendly, and they may have an interest in trade but not in us. And they may have such an extensive experience with other cultures already that we would simply be another tribe of many, of little intrinsic interest to them.