Hi nin64 -
Usually it's the one (or two) that you do regularly, and usually without effort or thought. It comes naturally. Most people have been utilizing their ability or abilities since they were kids - but they didn't have a name for it - and they grew up with it, so it's the 'norm' for them.
You can look up definitions of various abilities, and see which one (or ones) that resonate with you - such as "Oh, I do that!" or "That happens to me!" to give you a starting point.
Once you have narrowed down what you feel are your abilities, you can explore those some more - take local classes, or read more about refining those abilities (there are books out there for just about everything now! - and a lot of the books often contain information on more than one ability); or read online.
A lot of times when one begins exploring, they come across another ability that they weren't consciously aware of having. To me, it's a really neat adventure in discovering more about self.
Happy exploration!
