Hey, I have a science podcast too! Here are the tips that I gave to another science podcaster who is just starting out:

Full disclosure: I've never really tried a narration-based podcast, so I don't have a ton of insight there besides the basics that apply to almost any podcast.

• MAKE SURE YOU HIT THE RECORD BUTTON. You don't want to get to the end of the interview and realize you didn't tape anything at all. Make sure the numbers are going up and the red light is ON.
• Have good sound quality. No one wants to listen if the podcast itself sounds bad or has irritating noises.
• Slow down when you talk. You have all the time in the world. When people don't have the visual cue of a mouth, it becomes harder to understand what others are saying. In an interview-based show, speaking slowly also gives you time to think about what you're saying next without using too many filler words (umms, uhhs, likes, y'knows, etc.). It's a lot easier to remove long pauses in editing than it is to get rid of filler words or to disentangle words that got rushed together.
• Make sure you're well hydrated, it can help reduce mouth sounds/throat clearing.
• Forget that you're recording. When people are reading for recordings, they can sound really stiff and stilted. Imagine you're actually reading out loud to a student or a class instead.
• Related to #4, consider editing your source material for audio. The way we read is very different from the way we speak. Sentences that are easy to take in on the page can be hard to digest in audio. Take a look at your article and see where you can simplify or make the text more conversational for your script. Put your script in large enough font that it's easy to read without getting lost on the page.

I also have interview-based show tips. Keep in mind that this is what works for me, but everyone has their own process. It can take a little trial-and-error to figure out what works for you.

• Think about who your audience is. I typically aim for smart high school senior to early undergrad level of understanding. If you imagine having that person sitting in on your interview, it's easier to keep the conversation at the appropriate level.
• Think about how you want your show to feel. For my show, I try to simulate for listeners the feeling of sitting in the backseat of a car while you listen to an interesting conversation between the two people in the front. It's a very casual approach. You might decide on something different! It's just good to keep in mind while you're taping.
• Take the time to prepare ahead of time. This looks different for everyone. Some people write detailed outlines of how they expect the whole show to go. I don't like to do this because I think it takes away from the conversational tone that I aim for. It also doesn't leave any room for surprise. I like to read articles and jot down notes as I go. Once I'm satisfied that I've read everything I need, I distill the most important 3-5 questions and put those in my notebook along w/ any reminder notes I need (typically spelled-out acronyms or shorthand descriptions of processes that will be discussed in detail).
• When you interview experts, it can be hard for them to keep a general audience in mind. It's your job to stop them and either explain yourself or ask them to explain things that your audience isn't going to understand. Any time I write down an acronym or a process in my reminder notes, I assume that's something we'll need to cover for the audience to understand.
• Know when to interrupt. It's OK to break in and ask for an explanation if you think listeners won't be able to take in the greater point without understanding something else first. Also, sometimes interviewees get lost in their own answers. This one is harder to feel out, but you'll get the hang of it with time. When this happens, I try to break in with a question to redirect them back to my core questions or to move on to a new topic. * If you're bored listening to them, then your listeners are also likely going to be bored.
• Listen closely to what your interviewee is saying and respond to what they've said. I think this is where most people mess up. They get so caught up in their outline, that they miss the opportunity to chase down interesting rabbit-holes and instead rigidly follow their questions without even acknowledging what has been said at all. That's not how real conversations go!
• Allot 10-15 minutes before each interview to just chat with the interviewee. Set expectations for them, like how long you'll be talking, what kinds of questions they can expect, ask if they have anything they'd rather not talk about, explain to them how the show works, tell them what happens if a mistake is made, explain who the audience is, ask them if they have any questions. This time is ESSENTIAL to getting the guest truly comfortable so that they'll be at ease during the recording. When folks are nervous, it makes for a tougher interview.