Check with the local high school guidance counselor and find out what heavy equipment schools are in your area or state. Ask for recommendations for specific schools. If, for instance, you want to learn to operate a bulldozer, some courses may be better than others or only offered at specific locations.
Inquire what heavy equipment courses are available at your local technical or community college. Apply well in advance, and put your name on a waiting list if there is one.
Ask friends, family members and neighbors. Put the word out that you are looking for a heavy equipment school. Personal recommendations can often serve to be very insightful.
Go to a construction site and ask the heavy equipment operators there where they received their training. Inquire if they would recommend the courses they took and then follow up on their leads.
Do online research. Suppose you want to train as a backhoe operator, type "backhoe heavy equipment schools in Idaho" into a search engine and see what comes up. Bookmark the site you want to revisit.
Inquire at the local union office and see if they know of any heavy equipment schools.