Make sure you have in place:
Release Forms for the Artist/Personality or know them personally. You may utilize an email which outlines your show, and what they will be doing. I.E. a guest, what you will be discussing and their return email stating that they will be there, understand, etc. can act as an agreement or have a perfessional agreement written.
Contracts - Are you selling airtime commercials - make sure you have an agreement which outlines what you are providing, how many times the advertisement will be run, or where it will be placed (display ads) and how long it will run. Size and cost are also important to include in your contract.
Show Concept - It is a good idea to determine what you are discussing with your guest prior to your show, they will be more comfortable and preparation of questions allows them for formulate ideas for answers everyone is not good at off the cuff answers, it will make your show flow more smoothly if they know what will be asked during your interview.
Give Details - What, When, Where, How, Date, Time - THEN CONFIRM, and confirm again. It is amazing how many people forget they have an interview, make sure your guest (s)know where they are going or calling, what day, how long the interview will last, what time. Once you have given them all the details, be sure to confirm before your show. To be safe send another email the evening/morning before and then call (in case they didn't check their email).
TIP: Reinforce your start time, if you are taping. People are always late, so give yourself and your guest advance time to get in place before your live interview begins.
Never be late to your own taping. Never leave your guests wondering if they are at the right place or have other details confused like day and time. It makes for a nervous guest, and a strained interview.