Every DJ must at some time face the critical questions of why people listen to radio. The reasons are as follows: to hear music not in their personal collection, to be introduced to music they might like to add to their personal collection, to avoid silence (i.e. just to have something on), and most importantly: to create the illusion of human interaction. That's the most fundamental reason why even commercial radio stations still use real live DJ's and not machines to keep them on the air.
Your on-air personality, your wit and comment, are as important, if not more important than what music you play. It's your job to keep the listener's interest, to capture his imagination, to have him eager to hear what you're going to do next. You must constantly be creative in your approach, genuinely excited about what you're doing.
Implicit in all this is the idea that you should not compromise your personal integrity just to put on a good show. Never pretend to be something you aren't just to sound cool. It's not worth it. The Golden Rule of Radio is: "If you're having fun doing your show, your audience will have fun listening." Corollaries to the Golden Rule include, "If you're bored doing your show, your audience will be bored as well, and then stop listening." And "If you're forced to play certain things during your show and don't like it, your audience will not enjoy being forced to listen either, and will stop listening."
I should also point out that to a certain extent, radio is interactive. By that I mean that given a live on-air DJ who first announces the station phone number and second, is willing to take calls, the interested listener always has the option to call the station. The listener can talk to the DJ, ask questions about the musicians and songs that have been played, request other musicians and songs to be played, give critical feedback to the DJ, etc. Obviously, this is only possible with a live DJ, but it also requires that the DJ be highly competent in two areas: First the DJ must be able to continue doing his show while minding the phone (which can be quite difficult and hectic) and second, must have a sufficient understanding of the music she is playing and that is available in order to be able to have an intelligent discussion with the listener.
This is one of the reasons why new DJs usually do not get the best time-slots for their shows: so that the most listeners get to hear the most experienced, most well informed DJs. Therefor, from a Program Director's perspective, awarding time-slots to DJs should not only be based on straight seniority, but experience, talent, and technical and musical proficiency.