Paganism tends to be very much about the Journey rather than the Destination, and as there is no root Dogma, we tend to be incredibly flexible when it comes to Deity. Someone once remarked to me, Paganism was very much a practice of perception, and I would have to agree. There are many out there who follow Bast, the Egyptian Lady of Cats, but I can guarantee you, each of them will view Her in a different light, or have an individual relationship with Her.
Within Paganism you usually see a duality of Deity. On one side you have the Goddess, or the feminine aspect, and on the other side you have the God, or masculine aspect. This is not always true however. I myself do not follow a specific Goddess. I follow only Freyr and ask Him to intervene for me when needed, or to if He cannot, to pass the task off to someone who can. From what I’ve seen, many do the opposite, picking a specific Goddess, but with no specific God. Still others change who they call upon based on what they need. There is no right way to do it.
As to how you actually pick your Deity, the best way I’ve found is to see who speaks to you. I began to know Freyr through my dreams, but do you hear a small voice when you’re alone, or trying to solve a problem? Has someone every caught and held your attention? Take some time and just sit in silence. Wait. Listen. Who talks to you? Is there a particular culture that’s spoken to you, or you find yourself interested in? If you’ve already found your Deity, who is it? Did they choose you, or did you choose them? Why?
Link to list of researched Deities