Wow, that's not a wide open question?
I think I would go with the Beerguy's forumla. Find person, sell photo, collect money.
Okay seriously. And believe me, this is only some ways. First you can google "stock photo's". Go to stock photo companies and read their submission or sales policy.
Look for local areas of interest. For example, if you had a $5000 500mm f/4 lens and took pictures of the local football team during a game, I'll bet you would have the best photos in town and the players, parents and yearbook commitee might really want them. Maybe even the local paper.
Check your favorite magazine. Read their submission requirements. For instance, I am now in the photographer pool for a nature magazine. One of 200. They instructed me on their requirments for submitting pictures. When they need a specific picture they will actually e-mail me what they are looking for and that they are accepting submissions. Only those in the pool are allowed to submit. The last request was for pine marten. I couldn't find one. The only picture I have had published was of a weasel in a bullberry tree. I recieved $300.
You can do photoshoots. I did one of a girl and her horse before a horse show. Also weddings and graduation.
One thing that's most important. No one wants to buy crap. If you think your pictures are good, campare them side by side to a pros. If they don't stack up, you won't get paid. I don't care if you have a shot of a monkey screwing a buffalo. Exceptions are made of course if its Brad Pit or George Clooney sccrewing the buffalo. And Paris Hilton or Brittany Spears getting screwed by buffalo has been way overdone.
Mike