Use the connections/network you have and search for a way to include photography in it. For example, if you're an amateur musician then specialize in concert photography. Let the other musicians know that you're considering photo as a pro career and they will most likely spread the word. A friend of mine travelled all around the world participating in dog shows. Her network was huge (judges, breeders, owners etc.) so when she decided to start as a pro pet photographer the people in her network spread the word to help her out. Needless to say she has no problems getting assignments.
Check the competition in your area. Where I live there's only 1 pro photographer, and he's only shooting weddings/ceremonials and studio portraits. I am an amateur myself, but I sell a decent amount of photos simply because I am the only one offering my services in product/nature/landscape/press and concert photography. Unfortunately I don't have the guts to quit my job and go professional, so this means I have to say "no" to many assignments.
Kind regards
.lars