Talking directly into a diaphragm of a microphone will cause a nasty side effect called "P-popping". P-popping is a horrible explosive bass "thump" you hear when a speaker uses certain letters (P's and B's) and speaks right into the mic. You cannot remove P-pops from the audio once its there. When speaking into a microphone, you should talk "across" or just over the microphone rather than directly into the diaphragm. This will eliminate a good part of this problem. Another solution to P-popping is the use of a Pop Filter; these are large circles you place in front of the mic and are not visually acceptable in live situations. To help reduce (or in many cases eliminate) this low frequency distortion, simply roll off the low frequency response of the microphone in use. Keep in mind that the human voice has little (if any) energy under 120 Hz, so rolling off the equalization of that microphone will not loose any program response but certainly will eliminate the P-pops and handling noises. This is a trick used by the leading front of house mixing engineers.
It is very important to keep a source at the same distance from the mic so the volume of the source does not change drastically over the PA or in the recording. It is critical in vocals to keep the lead singer "out front" and at a relatively constant level. If a singer moves his head around a lot in front of the mic, the level will go up and down, making the singer loud and then soft, understood and then not understood. So practice keeping your mouth at the same position relative to the mic as much as possible, except when you really belt it out and need to back it off a bit. One huge change in the level and pattern of the microphone will occur if you cup your hand around the ball or where you speak into. Hold the mic on it's handle, not the ball.
Nearly all microphones make noise when you rub your hand on them or tap them when they are amplified on PA. This rumble or handling noise is impossible to remove. Cardioid mics can be a problem especially in the low frequency area. Professional sound engineers solve this by reducing the low end response of the vocal mic at the mixer. Most handling noise is in the 30-80 Hz region and since the human voice has little content there, rolling off everything under 80 Hz reduces the handling noise.
Mics sound different depending on how they are pointed at the source. Sources also have different response depending on whether you are directly in front of them or not. We spoke about "on and off axis" before, which refers to whether you are directly aimed at the center (on axis) or off center (off axis) of something. Pointing a mic directly (on axis) at something sounds very different than pointing it to the side of something (off axis). If a trumpet is pointed directly at the mic it sounds different than if it is pointed to the side of the mic. Same is true for acoustic guitars, pianos, singers, etc. Experiment!