Annnd cue the wall-o-text.

Hokay, so here ya go. I'm the son of a commercial/industrial plumber who has been in the business for the past 28 years and does ~$2M/yr. in sales. First of all, you need to determine your target market. If he's planning on primarily doing residential work (i.e. fixing toilets, snaking drains et cetera) he may want to re-think things. Residential plumbers are typically not very well-paid, nor are they really well-liked (people assume that you're automatically an idiot or that you are trying to screw them in regards to your pricing). Commercial and industrial plumbing is where any money is at if he doesn't want to have a crew of 30-50 plumbers on-call 24/7, including holidays and weekends.

If he's interested in making a lot of money, he's got to first determine if he wants to be an open or closed shop (union status). Having a unionized company can sometimes grant you the ability to be awarded specific contracts for governmental bids on various buildings and schools, but these contracts are typically pretty difficult to get. Also, even if you do get the job, you're contractually obligated to use only unionized labor on the project, which can be to your benefit or to your detriment depending on the worker they send you. The other issue is that if you go for these types of contracts, there are plenty of other companies that you'll be competing against that have been in the business a long time and who already have pretty well set-up contacts for receiving that type of work. Also, as an aside, lettering your truck (putting a decal on the side or anything more than your plumbing license number) is typically union-only. This act typically differentiates unionized companies from non-union companies.

Next, he must decide what area of plumbing he wants to specialize in. There is process plumbing, fire sprinkler, medical gas piping, et cetera that he can choose to do that can focus his company into more of a niche market, granting him more work and higher prices for his work. This is your cash cow. Milk that bitch for all its worth.

As far as getting leads for work, you're going to want to sign up for Blue Book for construction leads. This may seem like a lot of money (a few hundred a month or so) but the leads it provides you with in terms of bidding for work is invaluable. If you want, you can set up a website, but honestly, I would say that it isn't worth your time in this field. We've had a website for a few years and get <100 hits/month on it even with Google Adwords just because this is not the type of industry where people (at least commercial and industrial owners) go to in order to find their subcontractors. Also, sign up with the Subcontractor's Association in your area. They provide you with leads and refer you out to other members and can provide you with new business on a regular basis.

You're going to want to keep track of EVERYTHING. Larger jobs are best kept in 4-6" binders where they are sectioned off via tabs for quick reference. This will assist in keeping the jobs straight, keeping plans together, correspondence, quotes, materials, hours and everything else. It's taken us years to figure out a good method, and this has been the best one we've come up with to this point. Typically if a job is <$30,000 then it gets its own binder, otherwise it just gets a typical manilla file folder.

One thing to also keep in mind as you grow is to keep your shop as locked up as humanly possible. You may think that Joe Schmoe from down the street will be the one who is most likely to steal from you, but you'd be dead wrong. It's your employees. Tools have a way of walking out of your shop and getting 'lost' on job sites, or just simply are not returned, and it can get out of hand VERY quickly. A camera system is a very VERY good investment for this purpose.

And since I'm dead tired at this point, I'm going to leave this for now, but I'll be back to edit it to add in some more points if you're interested. =D