There was a Star TrekTNG episode where Riker was caught by a species on the threshold of qualifying for first contact. Riker was part of a larger benevolent spying ring, trying to determine a lot of those very questions about the target populace. A lot of the episode revolved around the federation/enterprise crew trying to mend fences and convey the spying was benevolent and neccisary because of many of these very questions.
In a much less invassive way. I think you could make some headway by monitoring broadcasts. Though how much could you deduce without a firm grasp of the psychological, cultural and behavioral norms and ethics of the target culture im not sure.
Might be best to just wait till some majority threshhold of the geopolitical states on a planet have the capability of approaching you, and then make your presence known. Let earth initiate dialogue to your federation.
Wait till there has been a launch from each major region that can reach the moon. Then setup a probe on the moon, broadcasting something that looks like a SETI Candidate signal. When humans open it, it broadcasts a signal strong enough to be recieved worldwide with instructions on how to intiate formal dialogue with the delegation on Europa.