Make sure to put out your cigarette before going to sleep.
Literal
Sleep before cigarette [possessive-の] fire [object-を] extinguish [so-that-ように] do.
~ようにする ('make sure to do X' / 'try to X') marks habitual intention. 火を消す ('extinguish a fire') — here applied to a cigarette. A sensible fire-safety reminder.