I'd add a bit more to "charge more", although it is a good place to start. The other half, which may be seemingly obvious, is "...for less time".
A higher hourly rate isn't always the best answer. Some clients require more managing than others, have poorly organized projects, or terrible schedule requirements. Any of these will destroy your ability to run a startup just as much as going broke. Pick clients that result in a low overhead for you.
I've cut my client list down from a dozen or so to just 2 big clients. One pays me a high dollar rate and is the sort of client who just shoots me an email saying, "hey can you spend 6 hours on this thing". The other is a long term project which is basically guaranteed work for the next 12 months or more. This is lower paying, but provides 20-40 hours a month of consistent work. Both clients are low maintenance, easy to deal with and flexible.
For me, it doesn't matter how big the hourly rate is if I'm getting hassled every day of the week. It's as much about your time as it about your income.
Not sure why someone down voted this, I think it's a good solution. Each time I had more consulting work than I knew what to do with, I'd raise my rates. Its a good way to throttle incomming work and either earn more money -or- what youre looking for: have more time for your startup.
I think I was too succinct. I'd disagree with "a good way" - it's "the way." Though you don't necessarily raise rates across the board, for every customer or every job. You do marketing. MARKETING.
Good customers, you explain your situation, raise your rates, but offer grandfather clauses if they're willing to guarantee some level of minimum work or pay upfront or with better terms. Bad customers, you double your rates overnight (and then do it again 3 months later). In between customers, you offer different packages that trade off them paying you more with them paying you more reliably, and/or offering you things that help you market your offerings better (referrals, testimonials, etc).
Additionally you specialize. If its something you don't like doing, you charge more. If its something that teaches you a skill that you can use for your nascent startup, you charge less.
Eventually if you're good, your "startup" becomes the R&D department to your burgeoning consulting business, and you've got something that feeds good things back and forth. The startup makes consulting more viable, and the consulting makes the startup more viable. Somewhere along the way you hire people.
A higher hourly rate isn't always the best answer. Some clients require more managing than others, have poorly organized projects, or terrible schedule requirements. Any of these will destroy your ability to run a startup just as much as going broke. Pick clients that result in a low overhead for you.
I've cut my client list down from a dozen or so to just 2 big clients. One pays me a high dollar rate and is the sort of client who just shoots me an email saying, "hey can you spend 6 hours on this thing". The other is a long term project which is basically guaranteed work for the next 12 months or more. This is lower paying, but provides 20-40 hours a month of consistent work. Both clients are low maintenance, easy to deal with and flexible.
For me, it doesn't matter how big the hourly rate is if I'm getting hassled every day of the week. It's as much about your time as it about your income.