As I've said before, when it comes to worldbuilding on an interstellar scale, your neighbors' choices can define your culture. This is especially true when a starfaring culture comes across a planetbound culture, because the starfaring culture is in complete control of defining the relationship it has with the planetbound culture.
So when I'm looking at my maps, when I see that a starfaring culture is going to come across a planetbound culture, I ask myself: what are they going to do?
Ignore: Let's face it, an alien species might fly by a planet, observe that a thriving-but-primitive culture exists on that planet... and shrug and move on. It's just not something that interests them.
Look, but don't touch: Here, the starfaring aliens show a bit of curiosity, observing the culture but not interfering with the planetbound species. At its heart, this is what Star Trek's Prime Directive is about.
Look, but don't... okay, touch a little: Like the above, but let's face it, to really understand the biology of an alien species, you're going to have to grab a few, poke and prod a little, run some tests, and then tag and release. And, hey, there are several billion of them down there, it's not like they'll really miss a few dozen, right? And it's for science, after all.
Preserve and Protect: This is taking "Ignore" or "Look But Don't Touch" to a more active level. Not only is one choosing to keep a planetbound culture uncontaminated, but they will defend it to keep anyone else from getting their filthy appendages on it.
Greet and Welcome: This is more or less the opposite of not contaminating the culture... it's showing up with the fruitbasket and saying hi, friendly-like, and being willing to let the planetbound species take that information and process it how they will.
Missionary: Look, these primitive people need help, you see? We're going to go down there and show them how to not make the mistakes we did, or teach them the best ways to make clean energy, maximize food yields, and educate their young properly. Look, it's for their own good.
Play God: Sure, the "missionary" method is nice, but it's inefficient. After all, you pretty much are like gods to these primitives, so just embrace that. Make a few proclamations from on high.
Open Trade Routes: Like "Greet and Welcome", you recognize the validity of this primitive culture, and are willing to treat them fairly in bringing them into an interstellar community. Or, you know, relatively fairly.
Benevolent Integration: The next level of Open Trade Routes, the primitive culture is welcomed, and brought into the interstellar community, as citizens of a protectorate of your empire.
Hostile Integration: AKA "Conquer".
Colonize: Just because this planet is inhabited doesn't mean we can't build here. The beaches are lovely, and they aren't using most of the resources they have! They don't even know what Lerian Quartz Crystals are for, so they won't miss them when we set up the mining facility. And these natives are just so adorable, hopefully they won't make much fuss.
Eradicate: The planet would be perfect for colonization, were it not for the infestation. Open fire.
Look and Touch. A lot.: These genetic experiments have to be done somewhere, right?
Any options I missed? Let me know.