Whatever your mode of transportation, make sure you have directions to your target organization, along with a backup route, in case of unexpected obstacles like traffic or a subway delay. Also, have the telephone number of someone to notify in case you're running late.
If you can, perform a dry run a few days before your interview: Travel to your target organization and be sure you know how to get there—to the door—without getting lost. Planning ahead means you'll feel better about yourself, and you'll be more relaxed in the interview.