First and foremost, ARRIVE EARLY!
Regardless of how you are travelling, if it is scheduled transportation (plane, train, bus), you need to plan to arrive early.  Most airports recommend that you arrive about two hours before your flight.  Train stations and bus depots aren't quite as bad, but they still say try to get there an hour early.

If you get there early, you can sit around and read a book.  If you arrive late, you're out of luck.  They don't hold flights because someone hasn't checked in at the terminal, and don't expect a refund if you miss it.

If you are driving, you don't have to be on time to pick up the car, but you do need to plan for traffic.  If you need to be to the con before registration closes or your favorite actor has his first panel, plan some extra time to ensure you're there before the show kicks off.

Remember:  "Lines will happen."