Here is an interesting paper posted on an Lassen National Park NPS website.

It describes the "lightning position", discusses the best places to be (and not to be) in the backcountry. The section titled "Reducing Lightning Risk In The Backcountry" on pages 4-6 are most important to hikers.

It is a 9-page PDF file:

Backcountry Lightning Risk Management
by John Gookin
Curriculum & Research Manager, The National Outdoor Leadership School