There is a ton.
Here on HN look for bdunn, orangethirty, maybe michaelochurch
Start with the first two and their blogs, Brennan is probably most focused on the area (doubleyourfreelancingrate.com gives you a hint)
Its generally not too complicated to say, its hard to actually implement:
1. build up a buffer of cash. Don't spend too much
2. build up a reputation or valid authority on a particular subject. (Do not Bullshit here. But you do not have to be a world leader either - just genuine). Choose something like HTML5 video codecs or PHP templating or something you are more than unusually interested in.
This is called content marketing as well - you write your blog and your self-published book and become an "authority" on a small area.
3. Keep your networks fresh - get in touch with all those LinkedIn contacts from the job two years ago. They will be people willing to push work your way, but only if you have a defined offering that makes sense for them. Keep in touch and do not ask anything - the idea is not to turn up after two years with cap in hand.
4. Offering - what is it you do? Don't say write software cos that's not an offering, thats a cardboard sign with "will code for cash" on it. Find a Niche. Industry? How is your knowledge of the automotive industry? Business Process ? Are you interested in CRM and web site optimisation? How about accounts packages in car factories?
5. Really find your offering. GO back and think again.
6. Test out the offer. Adwords might help.
7. Find (local) businesses who meet your criteria. Arrange meetups, webinars and other things and promote those.
(Something about cross promotion here)
8. Talk to a lot of recruitment agencies about jobs you dont want cos the above is taking a long time.
9. Realise that selling consultancy and selling products are pretty much the same thing - a clear offering with a good set of marketing to pull people into the point where they say yes.