John gives some solid advice but I believe your individual circumstances will change and, yes, dictate how you go about this.

One thing I would disagree with tho is the schedule aspect. I'd suggest one, at least when you're starting out. I found that I enjoyed doing art at home better than in an office atmosphere because I felt much more free to experiment. Not that I'd miss deadlines, I just felt more comfortable with the work. But also with this comes the "18 hour day" for little reason than you were "in the flow". Setting up an initial schedule will help with this, at least until you run into the inevitable "impossible" deadline.

It also depemds if you live alone or have a spouse, family or roommate. The big "problem" I see with your situation Dave is your upcoming offspring. Children change the situation very drastically, as does a pregnant wife. A friend of mine in a similar situation almost lost his house because of the "quality" time he spent with his family. His thoughts were that he could cater to the every whim of the wife and new baby and work while they slept. What he found was they were never asleep at the same time and that a person can only function properly for about 36 hours with no sleep. And the work tends to suffer a bit too.

The good thing is you're actually thinking ahead, inquiring from others and trying to set things up in a manner that will be beneficial to you. God luck and have a great time. 

Since you asked for specific methods, try playing two roles, that of the "boss" and that of the "employee". At the end of the day, switch to "boss" mode and review your day objectively. As boss, did your "employee" get an acceptable amount of work done given how important it all is? Would you have been pleased with the day had you actually paid someone else to do your job?

The self discipline thing seems easy at the beginning, but it can slip slowly without you noticing it.

Good luck!

Dave:

Wear pants.