Is being on time almost impossible for you? If so, you are adding enormous amounts of unnecessary stress into your life.
Driving to work or an appointment when you are running late means you'll arrive at your destination with stress hormones coursing through your body.
It's easy to underestimate the amount of time you need to get somewhere.
Try working backwards from your appointment time to more accurately determine exactly when you need to leave.
For example...
Let's say my flight leaves at 11 a.
m.
on a Monday morning.
I want to be checked in and at the gate an hour early (10:00) so I can browse the bookstore and get a snack.
This also gives me a good cushion in case of a problem; this cushion is crucial to being on time.
I'll estimate that the check in line will take me 15 minutes (9:45).
The security line is about 30 minutes (9:15).
I'm going to allow 15 minutes to park and take the shuttle to the airport (9:00).
  Traffic at 9:00 might still be a bit heavy, so I will allow 30 minutes to the airport (8:30).
  It takes me about an hour to get myself ready and out the door.
I set my alarm for 7:15 and I plan to be on the road no later than 8:30.
Better an hour too soon than a minute too late.
~Famous Old Saying Pinpointing the amount of time needed for each specific step of getting yourself somewhere on time helps you keep an eye on the clock to ensure you are where you are supposed to be in order to get to your final destination on time.
If chronic lateness plagues you, it's actually better to be a bit pessimistic in your estimations - assume there will be some traffic, plan for a wait time, prepare for the unexpected.