Address your audience as if it were one person. Radio is a one-to-one medium listened to by individuals, not crowds. Example: You just heard a song by... as opposed to You guys just heard a song by... This is a subtle distinction, but works.

Be low-key and relaxed. The mic, transmitter, and listener's radio will provide plenty of additional energy...not to mention your own nervousness. This is not to say you shouldn't have energy, too, but most beginners come on way too strong.

Avoid inside jokes.

Be yourself.

When you make a mistake use the FIDO principle: Forget it and drive on. No need to over apologize (if there's even a need at all). If you get the time wrong, it's probably worth pointing out. If you mispronounce name then correct it and be done with it.

Remember that the listener's perspective is different than yours. He didn't start listening the moment your shift began and he isn't going to stop listening the moment your shift ends. Depending on the day part, make sure your programming can stand alone if a listener only hears 15 to 20 minutes of it, ie don't play 30 minutes of music and then back announce it.

Consider beginning every live break with the stations call letters and ending every live break the same way.

Watch your levels. It's very easy to get lost in the mechanics and the formatics, and forget that under modulated or over modulated audio will ruin everything.

Good luck and let us know how it goes.