Sorry, Dozey. I posted a long reply and put a couple of email links in that gave a bit too much info about me in RL so I asked MNHQ to delete. I'll pm the links to you and try to remember the gist of what I said.
freelance photographer suggests to me that you want work as a newspaper or magazine photographer. The other possibility is business photography for websites and brochures. I have a friend who works in this field and she tells me competition is tough and it's a difficult niche. You would probably want to keep up the day job.
Given your question, I'm thinking more that you want to sell photos to individuals. Portraits or landscapes perhaps?
If this is the case, I would suggest you consider your skills and potential market. My DP is a keen amateur photographer and exhibits and sells his work (I'll pm a link to you). He deals in landscapes so has to find a shot he thinks will sell as well as a way of getting it to his market.
If you're looking at portraits then I guess you need to be presentable and reliable. An ability to put people at their ease and deal with screaming children would be a definite advantage! I have a friend in the US who is just starting a portraiture business and she also covers events. Again, I'll pm you a link to her website for ideas. She has thought about what her customers might want and has put together different packages.