Because rules are simple, they should be easy to maintain. A good quality rule should last a long time, as long as it’s looked after.
Ensure the rule is clean and dry before storing. They can usually be cleaned with soap and water or a mild solvent. Metal rules can have a little bit of oil rubbed onto them, occasionally, to help prevent rust.
They should be stored flat in a drawer or toolbox, so they won’t get bent and the edges won’t get damaged. Some rules have a hole or clip so you can hang them safely out of the way. Folding rules and digital angle rules should be folded up to store.