Naming Conventions

Anyone have any good systems for naming files and folders? Other than being consistent? Is it just personal preference or are some naming methods more useful than others?

‘/c/c01.css’
‘/c/default.css’
‘/css/master.css’
‘_css/default.css’
‘/i/’
‘/img/’
‘/_i/’
‘/s/nav.js’
‘/script/’
‘/_js/.nav.js’