Not using for a long time: Fully clean and strip down than repackage in their boxes.
Not using for days/a week: I sit it on some kind of holder, either a mod, the ohm reader, or one of my stands.
I have 4 tanks sitting in their package right now. 4 tanks in rotation all juiced up and ready to go. Thinking about doing a PIF at some point, I got a couple mods and tanks to get rid of.