Sooner or later just about every musician ends up in front of a microphone. On a gig or in the studio, the goal is to faithfully capture your instrument’s soul. Whether your performance ends up number crunched into digital posterity or blasted to the minions in a club, concert hall, or open field, placing the right microphone in the right place could mean the difference between magic and musical mayhem. Incorrect miking could turn a pristine guitar sound to mud or a gleaming Bach trumpet could end up sounding like a kazoo.
The first rule of thumb is to trust your ears. An experienced audio engineer will put their ears right in front of the instrument and find the sweet spot. (Not drums. Place your mics and beat a hasty retreat.) Every instrument projects sound off its surface uniquely. Get to know the characteristics of each instrument and where the best sound emanates from. Getting to know the sweet spot and how to get the mic into position, without interfering with your movements, is as essential as making sure your strings are fresh or your reeds are supple. Work with fellow musicians and engineers; experiment and listen.
Generally speaking, use dynamic microphones on stage, condenser microphones in the studio.
Dynamic mics, like a trusty Shure SM-57 or SM-58, can take a beating. Two inherent characteristics make them perfect for gig situations: they are less likely to feedback and bleed.
That’s right. That clunky old diaphragm, coil, and magnet technology championed back in the 1800s is lousy at recreating high frequencies and only really effective up close and personal. A dynamic mic’s tight cardioid (heart-shaped) pickup pattern rejects sound that is off axis and farther away. Perfect, if you don’t want drum hits and crunchy guitar chunks polluting your lead vocal mic. So, on the gig, put a dynamic mic as close to the source as you can get it. In fact, if you want to pick up some nice low frequencies, get within an inch. It’s called the proximity effect. You’ll pick up a couple of decibels of sweetness way down low.
Don’t be concerned about getting enough high frequencies to pass on to the PA system. A dynamic microphone will do the job. It just won’t be as sensitive to those high pitched tones that tend to entice feedback. Speaking of which, do not face the business end of any microphone directly into the path of any speaker: monitor or front end. You’ll only do this once or twice before you realize just how painful feedback can be.
Can you use a condenser mic on the gig? Sure, and you should, if you want to capture the high frequencies of drum kit cymbals. But, unless you’re in a controlled concert setting, or in the studio, dynamic mics, for the most part, are both less expensive and better suited for the road.
Now, for studio use and controlled concert settings, condenser mics are just plain better. Their delicate design characteristics make for a much smoother response and sensitivity to sound. The most important thing to remember about using them is that they need phantom power to work. Most mixing consoles and many microphone preamps have a switch, sometimes marked with +48 V, to supply voltage to the microphone’s capsule.
Positioning a condenser microphone is much different from placing a dynamic microphone. They also need to be treated with a little more care. Because they are so sensitive to sound, you don’t need to be as close to the source. Think of them as you would the human ear. As a matter of fact, when miking an orchestra or a choral concert, typically we would use a pair of high-quality condenser microphones in an XY pattern or placed at about a 90 degree angle to simulate human hearing.
Both condenser and dynamic mics can be found with a larger diaphragm. A large diaphragm will give a smoother lower frequency response. If lower frequencies are an inherent part of the instrument’s tonal characteristics, consider using a large diaphragm mic. It will make a kick drum sound a little richer, and vocals, strings, and wind instruments will sound warmer.
A good mic kit will have a mix of microphones, each with its own unique attributes. Finding the right tool for the right job is an exercise in experimentation. Many times in the studio, a number of mics are used to capture all the characteristics of an instrument. Trust your ears, but you can start with these simple guidelines.
Vocals:
On the gig, get up close and personal with a dynamic mic. In the studio, use a large diaphragm condenser microphone. Back up six to 10 inches (further back for opera singers), and you should consider using a pop filter (a light screen between the singer and the mic that prevents the wind made from pronouncing words with “P” from creating a pop sound).
Acoustic Guitar:
On the gig, most acoustic-electrics are fine plugged in. In the studio and certain concert settings, place two condenser microphones in front of the instrument. Put one about three or four inches off the neck, right where the neck meets the body. This will capture the bright, glistening tone of the strings. For richness of tone and low frequencies, find a sweet spot for the other mic near the sound hole. (Try a large diaphragm here.)
Brass Instruments:
Most of the sound comes out of the bell. Blow right into the dynamic on the bandstand, but in the studio back away from a condenser mic to get a full sound.
Flute:
On the gig, have the flautist step up to a dynamic mic and put their mouthpiece near the mic, being careful not to blow into it. In the studio, use a condenser and find a sweet spot over and away from the instrument.
Sax & Clarinet:
The sound emanates from both the fingering holes and the bell, so the best sound will come from a condenser microphone six to 10 inches or more away from the instrument. In a pinch on the bandstand, use a contact mic or a dynamic mic up close.
Grand Piano:
Two condenser mics: one for the high strings, one for the low. Experiment with mic placement. Mix in stereo.
Violin & Viola:
Use a condenser mic and place it above the violin and out of the way of bowing. Be careful, the closer you get to the action the more “rosin” you will hear.
Cello & Bass:
Get in front of the instrument, find the sweet spot and put a large diaphragm condenser right there. For deep rich tones, it’s usually below the bridge and slightly off to the side. 
For intimate concert settings of acoustic instruments, there is nothing sweeter than capturing all those delicate tones, just like you were performing in a studio.
Drums:
On stage or in the studio, use a pair of condenser mics over the drum kit to capture the cymbals. Place a large diaphragm dynamic mic inside the hole in the front head of the kick drum. Place an SM-57 right near the head of the snare. Use dynamic mics near the head of each drum and the hi hat. In a pinch, overheads and a kick drum mic will suffice. 
