I sometimes get asked for advice on writing non-fiction, either for the women's magazines or for a wider market. It's not my area of expertise - I have written and sold a few non-fiction articles but it's not really my thing.
Having said that, I can point those who are interested at a few blogs and magazines which are packed with good advice for non-fiction writers.
Firstly - I'd recommend subscribing to at least one of the major writing magazines. If you subscribe to Writing Magazine you will also get Writers' News each month. WM is full of useful articles for beginner and intermediate writers, and WN is full of market opportunities, so between them they cover the bases.
Writers' Forum is an excellent magazine and my current favourite, but is possibly geared a little bit more towards fiction, though they run a good feature on writing for a different market each month.
Then there's Freelance Market News, published by the Writers' Bureau, but anyone can subscribe even if you are not a WB student. As WB specialises in getting new writers published, this magazine should be spot on for the wannabe non-fiction writer (it's not one I've ever bought so I can't comment on it at first hand).
Treat yourself to a copy of either The Writers' Handbook or The Writers' and Artists' Yearbook
. These not only contain listings of magazines and newspapers, their submission requirements and addresses, but also several useful articles on different aspects of writing. They're definitely worth the money.
Blogs - take a look at Julie P's Articles Antics, Alex Gazzola's Mistakes Writers Make, and Simon Whaley's Simon Says, all of which contain lots of hints and tips for non-fiction writers.
Alex's blog includes a long post on finding markets, here.
Finally, as with all writing, study your market well before submitting. Actually, when it comes to non-fiction, you should study your market before you even write the article. Then make your pitch, and write the article when you've been commissioned.
So that'll give you a good start. If anyone has more advice or knows of other blogs worth looking at, please let me know in the comments below this post.