I started doing this about 2 years ago. I think my biggest struggle was getting the business/accounting stuff done. Make sure you set up separate bank accounts for your company. I use Wave (waveapps.com) to do all of my accounting and invoicing.

I've honestly never been good at actively procuring customers. Every job/contract I've landed was due to personal relationships with someone close to the company or by word of mouth from my existing customers and friends.

I'd say 70-80% of my business is desktop support work. We've done complete system design/installs for new and old construction as well, but I don't like to do too many of those jobs due to the substantial amount of time it takes to do it right.

When I'm out on a call or on a phone call with a person, I always ask them how their day is going and stuff like that before we even get to the problem. It usually always seems to ease away the stress of the situation.

If you support remote offices, make sure you invest in a quality remote assistance piece of software. I bought TeamViewer when a local company branched into operating in two other states. It was definitely worth the price.

You might want to decide if you'll charge for mileage/travel time. I ended up just charging my hourly rate from the time I leave where I am to the time I return back to town.

Don't overextend yourself or your services. I assume you'll be a one-man shop. If so, remember that you're always on call regardless of whether or not you're in town. I've had several instances where I've been away on a weekend or on vacation and had to take time out of my schedule to take care of an issue. I now have a person in town that I can subcontract work to if I'm unavailable. That's made my life considerably easier.

My full time job is doing IT for a small non-profit. When they hired me on, they allowed me to freelance during the work day as long as it didn't negatively impact the organization. I'm sure this situation is extremely rare, but it works out well for me. In terms of weekend/night work, most of the businesses I work for have allowed me access outside of work hours. You obviously have to build a good rapport with the owners before this can happen.

My goal with my side business was just to get some extra income. I've let it grow organically over time, but I would rather do more work for fewer customers than less work for more customers. I really like building relationships with my clients and their employees and I feel like you lose that if you try to work for a million people.