I think there are two different kinds of galleries. There is the local ones, generally in smaller cities, that are sometimes connected to the local museum etc. These would be far easier to get into.
Then there are the commercial art galleries that are for profit. Their interest in you would only be if they think they can make money off your work. It is almost like renting real estate to them. Their walls have to make enough money to pay their rent and pay their employees. This is a lot tougher sell. Your work obviously has to be exceptional.
That's my limited knowledge.