If such a thing occurred, I think we should approach them with caution--they may want to enslave us or even worst--dissect us for the advancement of their science!!
Of course, given the level of tech they may have, we may have to listen to why they came and comply to their requests.
The question is, how will they treat US! Any alien that can get here is going to be so far ahead of us technologically, that we had better hope they are nice.