Four Ingredients of a Great Podcast
High Production Quality
Your podcast needs to sound good. This is one of the most important factors in making a great podcast. Some people may put up with poor audio quality, but bad sound will test the patience of most listeners.
Record your show in a quiet room. Learn to use software like GarageBand or Audacity make it "shine" in post-production. If you don't have the time or you're not capable of editing audio files, you can outsource the work to a podcast editor.
Invest in good equipment. You don't have to break the bank, but quality recording equipment can really improve the sound of your podcast. Little additions like a pop filter for your microphone can really enhance the listeners' experience.
Practice your delivery. Get comfortable recording your own voice. Listen back to your episodes and take note of verbal tics and other areas where you can work on your speech. Make an intentional effort to improve those weaknesses.
A Focused Message
Don't try to appeal to everyone. Zero in on your target audience and cater specifically to them. This will make your show more impactful and build a loyal audience who connects with your show on a deeper level.
Make sure you have a clear "why" for yourself and your audience. Why are you making this podcast? What about this specific episode? Why should they listen to your show? What value do you bring that they can't get elsewhere? Make sure these answers are clear in your mind and make sure they are clear to your audience.
Respect for Peoples' Time
Time is our most valuable resource. Don't ramble. Stay on topic and try to keep all "rabbit trails" relevant and meaningful. Some shows are more conversational and flexible than others. There can be some merit to that, but when in doubt stick to your topic.
Even for podcasts that are purely conversational and entertaining it can be off-putting for an episode not to have a clear focus. Many of the best "rambling conversation" podcasts find a way to tie it all together in the end. Whatever you do, make sure that your show is engaging. You wan't your audience to walk away feeling that time listening to you is time well spent.
Come prepared. If people are going to give you a chunk of time out of their busy lives, you owe it to them to put in some work up front. Have a clear purpose and organized talking points coming in. Be sure to include a short introduction to each episode; listeners deserve to know what they are getting into.
Consistency
Publish episodes on a consistent schedule. Weekly or daily is best. We're all creatures of habit and people want to feel confident that they can expect a new episode to fit into their routine. Consistency builds trust and loyalty in your audience. The tone and mood of your podcast is part of your brand; keep them consistent to build familiarity with your audience.
Not only does your show need to come out consistently, but it needs to provide consistent value to the audience. Maintain your quality standard without faltering. Always provide value to the listener (whether that's information, entertainment, etc.)
Conclusion
These aren't the only four ingredients for creating a successful podcast. It will also take a lot a time, hard work and audience engagement among other things. You may even be able to find exceptions to these rules. For example, Hardcore History doesn't publish on anything close to a consistent schedule yet experiences tremendous success.
However, if you nail these four areas, you are well on your way to making something great. Focus on keeping your podcast valuable, consistent, targeted and sounding great. Everything else can come later.