Most people believe that a microphone is a simple enough instrument that they don't even think about what can go wrong with it. You talk into it, it records you. However, in a similar manner to amateur photography, a little bit of ignorance goes a long way and can produce avoidably shoddy results. There are several quick and easy tips that can help people avoid the most common mistakes with a microphone without going into full-blown sound engineering.
One of the most world-changing things about the internet is that it gives normal people a global audience for blogs and podcasts. But just as poor spelling and grammar can drive people away from a blog, poor recording quality can ruin a podcast. Fortunately, you don't need to hire a professional editor to write a passable blog, and you don't need a recording studio to get decent audio for your podcast. The plastic mic that came with your computer certainly won't let you achieve truly professional results, but as long as it isn't actively bad most people won't care.
Holding the mic
It all starts with this. If possible, you'll want to use a microphone stand. A mic lying on a desk, especially the desk your computer is sitting on, will pick up vibrations such as the computer fan that will be audible in the recording. A mic stand also brings the mic closer to your mouth. I once resorted to making my own mic stand out of a bent coat hanger. Hold the mic if you must, but avoid holding or covering any part of the sensitive area. If you can wear a headset, you can listen to your recording as you make it to help avoid the other problems.
Breathing
One of the most irritating disruptions on any recording is the speaker's breathing, because when it does come up, it tends to be persistent. If at all possible, avoid letting the audience know that you need to breathe. It's very easy to accidentally exhale onto the mic, and if you don't control your breathing effectively you can even be audible inhaling through your mouth. Move farther away from the mic if these issues pop up, and try to inhale through your nose instead of your mouth. Even the Chocolate Rain guy knew to move away from the mic to inhale, although most people will not find it necessary to take it to the excessive degree which he does.
Avoiding plosives
The second most distracting thing I hear on amateur recordings is a puff of air that hits the mic whenever the speaker pronounces a plosive consonant, especially p and b. There are several ways to avoid this. You can put a cover over the microphone, sit back a bit farther from the mic, put the mic a little to the side instead of directly in front of your mouth, or hold a piece of a paper between your mouth and the mic. Avoiding this one simple mistake can set you a head and shoulders above most other amateur recordings.
Volume
Volume is important, but usually not critical. Your audience is usually willing to turn up their speakers if necessary. To some degree, you can turn the volume up on your recording with even the simplest audio editor, but if you need to turn it up too high you will amplify ambient background noise that lowers the overall quality of the recording. Most audio recorders can display a volume bar as you make your recording. You will get the best results by getting this bar as high as you can while staying below 100%. This would cause clipping, which means the audio wave will be cut off at the extreme ends. This results in critical nuances of the sound being lost as the input is saturated beyond its ability to record them. This is hardest to achieve if sound effects or other loud noises will be part of the recording. Remember that if you need to move back from your mic to prevent the other problems, you may need to speak louder to achieve the volume you want. If you're having trouble reaching the volume you need, check your computer's volume settings, you may have a microphone input setting you can adjust.
Radio voice
Most people record in their normal speaking voice. This is usually fine, but you may want to make some sample recordings in different voices to see what sounds good. Remember that your voice sounds differently bouncing around in your own skull than it does recorded and played back. Pay attention to enunciation, and try speaking from your diaphragm. Try not to slur, drop the g's from the end of your words, or skip over consonants that require tongue movement such as t and k. These bad habits people use in ordinary speech (some regional) can affect how understandable you are.
Preventing feedback
Feedback is a rare issue in podcasts, but for completeness I'll mention it. Feedback is caused by the microphone picking up signals from the speaker, amplifying them in a feedback loop. Usually recordings are not done with the speakers on, but this can be useful if recording with a headset (which will prevent feedback because the mic cannot pick up signals from the headphones). If you must leave your speakers on while recording, for example to hear your results in real-time, turn them away from the mic.
Editing
Slightly advanced, but not too difficult with modern point-and-click audio editing tools such as Audacity. Few people can talk or read for long periods of time without stumbling occasionally. If you do this, you don't need to start over if you can edit your recording. What I generally do is stop at the point where I stumbled and start the sentence over. You can mark this position by blowing into the mic or making another loud sound that will be identifiable when looking at the visual representation of the recording in the editing software. You can then select and erase the bad version of the sentence, leaving only the good version that followed it. Be careful to leave a short period of silence following the previous sentence when you do this, though, so the transition has a natural-sounding pause.
Now go forth, and amaze your global audience with your newfound recording skills. Or at least don't disappoint them by sounding like you don't know what you're doing.