Ok Complete, The first thing you should do is study every aspect of this profession. You should have a good working knowledge of basic electrical theory. You should know Ohms law, watts devided by volts equals amps. You should know how to make good connections. You should know how to go about designing a system for a property, taking into consideration, the home owners wants and needs. An older person is going to require more lighting than a younger person.
You can attain most of this information from a good lighting seminar. Most quality lighting manufacturers and distributors offers these from time to time. I suggest reading "the landscape lighting book" by Janet Moyer. This is the bible of the industry.
The one thing I will stress more than anything else is that if you are going to do this, you must do it right. Do not cut corners. Do not use cheap materials.
I strongly suggest joining the LVLIA (Low Voltage Lighting Institute of the Americas) www.lvlia.com
. They will give you a "Standards of Installation" book that will tell you how these systems should be installed. They are also the only non profit orginazation that has a certification.
Those are just a few tips to throw out there. Take the ball a run!!