I would advise working for an Irrigation company for a few years before starting out on your own. Learn all you can, get your licenses, liability, workman's comp etc. Check out this site for some pointers www.irrigationtutorials.com. There is good money in it but you have to stand behind your work and don't cut corners - they tend to bite you in the end.
Richard Kersten
S&R Sprinkler Systems and Landscaping, Inc.
Destin, Florida