Governments around the world would either get all protective or try to keep everyone calm. NATO already elected somebody who's the ultimate diplomat or something, who would be pretty much the one person who's allowed to speak with aliens if they show up. But I assume anything with the proper technology to get here before we do, unless they've RELIGIOUSLY tried, without stopping for things like war and trade, for the whole of their civilized existence, to get to other planets, and have literally no other weapons technology they could have developed, is worth fearing to some degree. And unless the entirety of the alien race was brought here, they're pretty much trapped lightyears away from their homes, they'll never, in their lifetimes, be able to communicate on long terms or see their homeworld again, unless they have absurdly long lifespans. They may have self-perpetuating life resources, or they may have run out, the time it took to get here, (unless they have warp or light speed travel) would require that they reproduce, they'd never get much non-inbreeding sex done by the time they get here, so they'd need to have evolved something to protect them from hereditary damages, unless they don't reproduce like we do.
What I'm saying is, these people would be detached and desperate, they might be jealous, insane, sad, willing to contact us just that much, or otherwise. And that's assuming their psychology and intellect is similar to ours.
There are far too many variables that come into play based on the behavior of the beings alone that would determine how I reacted. We're dealing with species that have evolved on entirely different planets, under different circumstances, they may have more or different elements than we do, they may be made out of different stuff, they may have different technology, or they're susceptible to different things, they might not even be made out of cells. The same with their ships. The very concept of what their ships do, besides moving around and how they do anything they do might be completely foreign to us, maybe they can't even survive our orbit because it's so foreign to them? Maybe their concept of life is so different that they think Earth is a dead planet? Maybe their intelligence is so high that we're oversized amoebas to them? Maybe they've been here all along, and our concept of life is so foreign that we think they're not living.
But if it was one of those disc-riding aliens that just so happen to be hostile, you'd bet your ass I'd get my baseball bat and yoyo, gather up my homeboy, my dog, a random chick with magic powers, a martial artist named after excrement, and a 50-year-old retired thief, and then murder the crap out of all of them using household weapons and psychokinetic magics.