"What Planet are We From?"

It's an interesting question and unless you are placing your campaign setting on an Earthlike planet in a solar system like ours, one worth exploring.  There's a lot to consider that will need adjusting if you don't use some sort of Earth analogue.  Just one sun?  How many moons?  How does this affect tides?  How close are other planets and how many are there?  It seems likely that unless you have a reason to not use an Earth clone, it might be the easy and maybe even the best choice from the perspective of player familiarity.  However, if you are looking to possibly do something unusual or unique, start with some basics from NASA regarding planets around other stars.