First, what can you do? What are your actual skills?
[for example, I can make a martini, say, or evaluate a journal article in my field]
Second, how necessary and valuable are these skills?
[this is the value that others place on these skills, humanity in general]
Third, how uncommon are they?
[If I can make a martini, but so can millions of other people, this skill is not going to be as highly prized. This factor is independent of the second criterion. For example, making a fried egg is a valuable skill, but almost anyone could be taught to do it.]
A fourth factor is more tricky to define. There are things that are not particularly valuable, in intrinsic terms, and not particularly rare. However, with certain skills, society has determined that the very highest level of development is immensely more valuable. Hitting a golf ball with a club, for example, lacks any social value, per se. Many people can do it, also. But doing it very, very well brings enormous economic benefits. You cannot get paid for hitting a golf ball; in fact, usually you pay for the privilege. A very tiny percentage of people who can do this better than anyone else, though, can get paid large sums of money.
Situations in which we give extraordinary rewards to ordinary skills provoke outrage. Say, speaking fees in the thousands, for those who are not great speakers.
A rare skill might not have any value for anyone else, so its rarity in itself brings no added benefit.