I stumbled across this via Hacker News. This guy basically explains how consulting works, with some great advice. Here’s three parts that stood out for me:

This is, far and away, the most important lesson to learn as a consultant. People who are unsavvy about business, like me in 2009 or like most freelancers today, treat themselves like commodity providers of a well-understood service that is available in quantity and differentiated purely based on price. This is stunningly not the case for programming, due to how competitive the market for talent is right now, and it is even more acutely untrue for folks who can program but instead choose to offer the much-more-lucrative service "I solve business problems -- occasionally a computer is involved."
I don't actually think this just a programming thing, and although I'm no longer in a position to be able to hire myself out on a weekly basis, the following approach sounds sensible:
If you quote hourly rates rather than weekly rates, that encourages clients to see you as expensive and encourages them to take a whack at your hourly just to see if it sticks. Think of anything priced per hour. $100 an hour is more than that costs, right? So $100 per hour, even though it is not a market rate for e.g. intermediate Ruby on Rails programmers, suddenly sounds expensive. Your decisionmaker at the client probably does not make $100 an hour, and they know that. So they might say "Well, the economy is not great right now, we really can't do more than $90." That isn't objectively true, the negotiator just wants to get a $10 win... and yet it costs you 10% of your income.
I always mean to ask for case studies, but never get around to it. He explains why it works:
I always ask to follow a successful consulting engagement with a case study. My pitch is "This is a mutual win: you get a bit more exposure and I get a feather in my cap, for landing the next client." Case studies of successful projects with some of my higher profile consulting clients (like e.g. Fog Creek) helped me to get other desirable consulting clients. Very few clients turn down free publicity, particularly if you offer to do all the work in arranging it.
Source: Patrick McKenzie