The interview consisted of the basic questions such as why do you want to work here, and how long do you see yourself with the company. The job is as entry-level as it gets, so if you manage to make it to the interview stage and do not get an offer, than the interview must have been a real disaster. Now, in saying it's an easy process, I don't want to give the impression that normal interviewing etiquette goes out the window. Dress nicely (I wore a suit), be prepared, and arrive 15 minutes prior to the prescribed time.
Entry-level UPS jobs are high intensity and not for the lazy. If there is any perception that you are not willing and able to do the job, then you won't get the position. UPS relies on EVERY employee to accomplish the mission, and if you are seen as the weak link, you won't last long.
Now as for being promoted to Part-Time Supervisor, it's a lot of memorization of key safety points. Just bust your hump for a little while and people will notice you. While there are some people who probably should not have been promoted to Part-Time Supervisor, don't let that discourage you. As one of my bosses told me once, at UPS the cream always rises to the top.