Determine how much time you can reasonably commit to scheduling guests, preparing interview questions and doing the actual productions. If you plan to work out of an existing studio, you will probably be required to work around the limitations of available time slots and utilize the facility's own technicians. If you plan to work out of your home, you'll need to invest in creating a quiet recording area, buying/renting equipment and determining whether you'll need to hire assistants.
Decide whether you want your talk show to be strictly audio or video and whether it will be done live or pre-recorded. These decisions will be based on your own comfort level in front of a microphone and/or camera as well as the desired frequency of the program. If you're doing podcasts, for instance, you may want to record four separate shows all on a single Saturday and then release each individual segment once a week. Perhaps you're doing all of your interviews on the phone which would give you even more flexibility in terms of scheduling chats with your guests (not to mention that you could work in your pajamas).
Identify the target audience for your talk show. If, for example, your radio talk show is going to be airing during rush hour, you can make the assumption that your listeners are traveling in their cars to and from their jobs. If your local access program is slated for late morning or early afternoon, your demographic is likely to be housewives, retirees and/or students. If you opt for a podcast, it's important to study your competitors' podcasts to discern who the content is designed to appeal to.
Identify a unifying theme for your talk show. Establishing the parameters of participation will make it much easier down the road to attract enthusiastic guests. For example, perhaps the target guests you have on your program are up and coming musicians who will be including samples of their music as part of the interview package. If it's a local access show, maybe your specialty is to invite guests who have unusual jobs or who like to do cooking demonstrations. If they have a good time being a guest, they're going to tell their friends and relatives which will, of course, result in great word-of-mouth publicity for you.
Make a list of your initial guests. (At the start, these may just be people you personally know who are happy to help kick things off.) Schedule time slots for them to be on the show. Again, this will be predicated on the format of the program and whether you will be chatting with them individually or as a casual panel in which they will be interacting with one another just as much as they interact with you.
Make a list of more interview questions than you think you will actually use. Every once in awhile, you're going to have a guest who answers everything in three words or less. If you have scheduled a 20-minute chat with them and they have already answered everything in the first 5 minutes, that's a lot of dead air you're going to have to fill up.
Prepare a working outline prior to the interview with rough estimates of how much time you plan to devote to each question or demonstration.
Relax and have fun!