I would imagine that if we found a new planet with basic life, we would move to a unclaimed continent and start to mine the shit out of it. When locals begin to protest at us undermining their culture, security will move in.

I would imagine a advanced lifeform would do to us the same. Perhaps wait until we have phaser weapons or sheilds before finding aliens :P At least find fossilised microbes on mars to put to bed how could life start from chemicals.