Get Into the Habit of Thinking Ahead
Most tips you'll find here (or elsewhere online) are based on the premise that we think ahead about our tasks. For example, do X early, estimate Y more accurately. But most of us are late precisely because we forget to think ahead. We look up the appointment's address at the last minute and realize it's farther away than we thought. Or we forget that our reservations are at the height of rush hour.
Thinking ahead gets into more overarching organization and time-management skills. But the biggest bang for your buck can come from this: In addition to packing those kid lunches, consider thinking over the next day the night before. (Or for true punctuality ninjas, look at the upcoming week on Sunday night.) Where do you have to be and when? Are there new addresses to map out online? Are there any really important events, like an interview, a wedding, or a kid performance or game? Anything scheduled back-to-back-to-back? Pinpoint the weak spots and plan (or reschedule) accordingly.