I've written/cowritten 3 books and a whole lot of articles over the past ~15 years on a freelance basis. Most of the good work came through an agency, StudioB, though I had pitched magazines and other places from time to time on my own.
My experience is that a lot of the good sources of ad-hoc work have dried up. That's not to say there is nothing now, but it's not the shooting-fish-in-a-barrel it was a few years ago. The demand has gone up and down over the years so I'm sure it'll be back.
As you've seen it's a lot of fun. I always treated it as a way to get other people to pay for me to learn the stuff I would normally have done in my spare time anyway. The money was good for the time invested, but I make far more just working a day job.
If I wanted to make an income from it, I'd be finding a company or two to attach myself to rather than piecework.
I've found that the industry is very focused on your portfolio, so continue to build upon that.
Also, be very nice to the editors you work with. They provide a lot of feedback to the people making the decisions, and no one likes a prima donna.
In general, I think it's fair to say that freelance writing has gotten tougher. A lot of the people who used to have full-time journalism gigs are now freelancing in various ways (or working for companies doing evangelism, editing, etc.) I'd also agree that the people I know who probably make the most money directly from writing get most of their business from a small group of clients.
However, for the vast majority of people I know who write computer-oriented books (including myself), it's essentially a branding exercise to support either their full-time employment or a consulting business of some sort.
My experience is that a lot of the good sources of ad-hoc work have dried up. That's not to say there is nothing now, but it's not the shooting-fish-in-a-barrel it was a few years ago. The demand has gone up and down over the years so I'm sure it'll be back.
As you've seen it's a lot of fun. I always treated it as a way to get other people to pay for me to learn the stuff I would normally have done in my spare time anyway. The money was good for the time invested, but I make far more just working a day job.
If I wanted to make an income from it, I'd be finding a company or two to attach myself to rather than piecework.
I've found that the industry is very focused on your portfolio, so continue to build upon that.
Also, be very nice to the editors you work with. They provide a lot of feedback to the people making the decisions, and no one likes a prima donna.