I have a small consulting business - write software for other people since I have yet to find that one product to develop for myself. I generally have just one client at a time, which does not allow my business to get to the point where I can quit my day job. Most of my work comes from referrals as I have yet to find a way to market my skills.
Any suggestions on how to take this to the next level?
Your overall earning power and security is limited if you are a single consultant. I started my consulting business with a partner which has made it a TON easier, I couldn't imagine having to do it all alone. Means you need more work initially but companies are more comfortable when multiple people are there to support them.
Off the top of my head:
Automate the work you do, so you can do it much faster. I'm in the same situation as you. Software dev, have 9-5, have other clients, but not enough of them.
I was on the same situation as you are a year ago. To get new clients, I focused my time and efforts on these activities: