Select microphones appropriate to the instrument or voice. For example, electric guitar amplifiers typically match with dynamic microphones close to the speakers, with large diaphragm condensers and ribbon mics sometimes used farther back. An acoustic guitar is best handled with small or large diaphragm condensers. For a singer, you may set up several large diaphragm mics in an array and try each to find the best match.
Play with mic placement once you decide on the best basic sound. Moving a vocalist close to a mic conveys a greater sense of intimacy in the sound, while farther back gives a sense of space. Many microphones respond differently when sound enters their capsules slightly from the side, referred to as "off-axis response." This characteristic is often used to fine-tune mic placement. Guitar amps in particular favor an off-axis approach.
Use controls on the microphones themselves as a first line of adjustment. Many mics include pads for high-volume signals. Switch these on when overloading preamps is an issue. Likewise, bass roll-off switches can help your recordings by reducing the subsonic frequencies captured where not needed.
Consider the microphone's polar pattern and how it may help you eliminate unwanted sounds. Finger noise on an acoustic guitar can be reduced by using a figure-8 pattern mic with the null (the dead zone at the sides of a figure-8) pointing toward the guitarist's fretting hand. When you have several players in the same room, arranging them face-to-face will place them each in the null of the other's mic when using a cardioid pattern. Omnidirectional mics allow you to pick up an ensemble seated around the room simultaneously.
Use stereo mic configurations when a wide sound source is encountered. Acoustic guitars and pianos are often miked in stereo when they are featured prominently. Ensembles and orchestras can be recorded effectively with two small capsule condenser mics in a stereo pattern.