Hi flowers,
You would ideally want to do a course which qualifies you to obtain public liability insurance.
The Sterex courses are popular:
http://www.sterex.com/Education/Training.aspx
Really, it depends on what you feel you want to get out of a course. Many who have read the important text books, own a machine and have been practicing on themselves/victims, absorb info from HairTell etc, find the courses on offer here too simplistic and often put forward ideas that we on HairTell at least may find issue with (“anagen only” perhaps?).
By far the most helpful thing would be to find an experienced and skilled electrologist willing to mentor you.
Personally, I would only do a course to obtain the insurance and therefore do the cheapest, shortest one I can find that offers that.