You've sent out a flawless résumé and cover letter, or you just nailed an interview, and now it's time to follow up. Don't make the mistake that only formal interactions matter!
If you're sending an email, make sure you edit it! Sloppy messages will get you noticed, but not in a good way.
If you're phoning or making an appearance at the office, make sure you are polite to everyone you interact with! Charming the boss but acting rudely to the assistant will not go over well, and could halt your progress.
Bottom line: always be your best professional self!