Here is a very basic, general procedure to keep in mind when miking something that makes sound: Use a microphone with a frequency response that is suited to the frequency range of the sound, if possible, or filter out frequencies above and/or below the highest and lowest frequencies of the sound.
Place the microphone at various distances and positions until you find a spot where you hear from the studio monitors the desired tonal balance and the desired amount of room acoustics. If you don’t like it, try another position, try another microphone, try isolating the instrument further, or change the sound of the instrument itself. For example, replacing worn out strings will change the sound of a guitar.
Often you will encounter poor room acoustics, or pickup of unwanted sounds. In these cases, place the microphone very close to the loudest part of the instrument or isolate the instrument. Again, experiment with microphone choice, placement and isolation, to minimize the undesirable and accentuate the desirable direct and ambient acoustics.
Microphone technique is largely a matter of personal taste. Whatever method sounds right for the particular sound, instrument, musician, and song is right. There is no one ideal way to place a microphone. There is also no one ideal microphone to use on any particular instrument. Choose and place the microphone to get the sound you want.
We recommend experimenting with all sorts of microphones and positions until you create your desired sound. However, the desired sound can often be achieved more quickly by understanding basic microphone characteristics, sound-radiation properties of musical instruments, and basic room acoustics.