1) Their survival will be more important than our survival.
2) Wimps don't become top dogs.
3) They will assume that the first two laws apply to us.
To expand;
If there is even the slightest possibility that we will threaten their survival, there will be elements of that species who will advocate eliminating the threat -- even if that means eliminating us as a species.
Any species that manages to claw itself to the top of a planetary food chain and develop the technology required for interplanetary space flight is going to be as least as tough, smart and nasty as we are. They may change philosophically, but the potential will most likely remain.
If they encounter another space-capable species, they are going to assume that species is as least as tough, smart and nasty as they are capable of being, and also assume that we may view them as a threat to their survival -- and act accordingly.