Work experience is the best thing you can do. Find a company that does many different things, maybe a commercial plumber.
What you want to do is get as much experience as you can.
The license will not come into play for at least 4 years of hands on experience.
A license will do you NO good unless you know alot about plumbing. To many people are licensed today and do not know what to do with it. Being a Licensed Plumber today is much more than having a license.
You have to know how to do it and you need to be able to direct others to do it. Experience in the trenches and alot of reading is the only way to get you ready for this. Have patience, If you go to quickly through this learning experience, your chances of failing as a business owner increases.
The Local Plumber
Tustin, California http://www.TheLocalPlumber.com