" As much as you can reasonably afford, plus regular practice. Once you have attained a decent level of skill, a good goal is to attend one two-day class per year to maintain your skill and keep your edge sharp."
What Pax said, but applied to firearms related and hand to hand related knowledge, skills, and abilities. Because the fight is not always of our choosing or the way we'd choose it.
Meriam Webster's: Main Entry: ci·vil·ian Pronunciation: \sə-ˈvil-yən also -ˈvi-yən\, Function: noun, Date: 14th century, 1: a specialist in Roman or modern civil law, 2 a: one not on active duty in the armed services or not on a police or firefighting force b: outsider 1, — civilian adjective