Typically, you must meet some sort of requirement that the individual has.
Also, keep in mind that not all NPCs are able to be married to.
You can find out what the potential spouses are, what their race, sex, location, and requirements are here:
http://elderscrolls.wikia.com/wiki/Marriage
Also:
Houses don't really matter because you have the option to move in with them when you are married.
But you can also allow them to move into your house(s) as well back and forth as many times as you wish.
But keep in mind, there is currently no way to divorce in Skyrim, so unless you look up one of the few ways to glitch out of it, it's permanent.