1. Be fanatical about using your own resources, not your employer's, for outside work. You're already doing this, but the point bears repeating. Emailing consulting clients on the company's system, or devoting time during work hours to meeting an outside deadline, can get you sacked.
2. Clearly define your availability. "Be upfront with your outside clients about the fact that you're working full-time and may not always be reachable during regular business hours," Cardinale advises. Tempting as it may be to let the boundaries blur, your full-time job has to be your top priority -- at least until you decide to leave it.
3. Don't bite off more than you can chew. Build some breathing room into your schedule so you don't burn out. "Consulting works on referrals. You want to have enough energy to give clients your best work, so they'll recommend you to others," Cardinale says.
Another reason not to take on too much at once is that "while you're still trying this out, it should be a positive experience, not one that leaves you exhausted," she adds. Don't worry about turning away business that, realistically, you can't handle right now: "If you set limits -- so that, when you do take on a project, you can give it your very best -- clients will actually respect you more."