Close miking obtains as much of the direct sound of an instrument as possible. The close miking technique tends to emphasize the presence of the instrument. It is particularly useful when other instruments are present in the same room, as close miking tends to reject the pickup of other sound sources due to the proximity of the microphone to the sound source being captured. With most close miking techniques, the microphone is within 3 feet of the sound source. In order to achieve the desired sound from a close-miked instrument, move the microphone around and listen for variations in the sound being picked up (while still keeping the microphone close to the sound source).
Ambient miking is primarily used to obtain the reverberant sound of the room. Although an ambient mic will pick up some of the direct signal from the instrument, it will typically pick up more room sound than direct sound. Typically, ambient mics add space and depth to a recording. Because of this, they are often blended with a close microphone in order to achieve a mix of the two.
Since there are great tonal differences between close miking and ambient miking, accent miking is occasionally used to strike a balance between these two techniques. For instance, when recording an ensemble with an ambient miking technique, you might want to single out one instrument during a solo. While close-miking this instrument might make the instrument sound unnatural, placing an accent microphone that strikes a balance between the direct sound of the instrument and the ambient sound of the room might be a more appropriate choice. Place an accent microphone close enough so that it picks the direct signal of the solo, but not so close that it causes that particular instrument to stick out. Most accent microphones are 3 or more feet away from the solo instrument; experiment to find the right distance for the recording.