I just wrote my first guest post ever. I've been writing all of my life. I've published a book. I've built and sold a publication. But I've only now written my first guest post.
My biggest concern, as with all I do, especially with writing, was making sure I was providing as much value as I could to the audience. So long as I accomplished that goal, I was sure that I'd be able to extract the value necessary to make it economically worthwhile.
My lone principle of content production: provide value to the reader. Everything else will follow.