If you miss a dose of trazodone, take it as soon as you remember — unless it's close to the time for your next scheduled dose, in which case skip the missed one and resume your normal schedule. Never double up to "catch up," since this increases side-effect risk without providing extra benefit.
If you're taking trazodone for sleep and miss your bedtime dose, simply skip it for that night rather than taking it later and risking next-morning grogginess. If missed doses become frequent — for depression treatment especially — mention this to your prescriber, since consistency matters for effectiveness.