To begin with, to make a bit of cash, it would probably be a good idea to stick to non-fiction. For a start, that's where I've made money in the past.
As an article writer, or for non-fiction books, it's a good idea to write about things that you know about or are interested in, so for me:
- voluntary youth work - Scouting, adult training, youth programme, good practice, development etc.
- child care - bringing up young children
- crafts with children
- wildlife and the outdoors
- outdoor leisure pursuits
- camping and caravanning.
The next stage in the process is to drill into each idea, come up with some ideas for articles, think about what publication or publisher might be interested in them, do the market research and get on with the writing!