Let's say you've read good reviews about the vocal microphone you bought for your home recording studio, and you're reasonably happy with the tone you're getting, but you wish that it was a little more responsive. There are a few ways to increase the sensitivity of your microphone and help make your vocal performances more vibrant.
Experiment with the trim control on the recording channel you're using. Gradually turn up the trim level while monitoring the pre-fader level meter. Try to get the level as high as you can without clipping the signal. This is the digital distortion that occurs with a peaking signal. It's decidedly unmusical and should be avoided at all costs.
Experiment with your technique on the microphone. If you're too far away from it when you sing, you will not get the most from it. If you're too close, you'll have issues with distortion.
Invest in an external pre-amp. The pre-amps in many mixing desks and digital interfaces do a good job, but upgrading to a higher quality external pre-amp can add substantial distortion-free gain to your signal and really bring your microphone to life. Some pre-amps offer a largely transparent boost to your signal, while others color the sound substantially. Which way to go is a matter of preference, and it pays to try out several models until you find one that suits you.
Add a little compression. Using a compressor on your signal will boost the level of the quieter-recorded passages while taming the peaks, adding a little spark to the sound of the microphone. When used sparingly, it can even out the sound of your recorded track and give you a consistent volume level. Be careful not to overdo the compression though; to do so is to risk losing the dynamics of your performance.
Take the foam windscreen cover off your microphone and instead use a mounted pop filter (see Resources). Foam screens tend to deaden the sound, while pop filters are more transparent and will help you control the hisses and pops from a voice without compromising the sensitivity of the microphone.
Experiment with EQ. Often rolling off some of the low frequencies and adding a little boost to the upper mids can be enough to give the microphone sound a little more definition and help it cut through a mix.
If your microphone is a dynamic vocal microphone, like a Shure SM58, you might reserve it for live stage work and buy yourself a condenser microphone for in-studio vocal work. Dynamic microphones are known for their sturdy construction and ability to handle extreme sound pressure levels, and while this is useful in the studio when recording instruments with such extreme levels, like drums and certain brass instruments, a condenser microphone has a better frequency range, is considerably more sensitive and thus more effective at capturing the intricacies of the human voice. When you set up a condenser microphone in your home studio, the difference will be immediately apparent. In fact, condensers can be so sensitive that they can easily pick up noises from neighboring rooms, so you may have to consider some sound-proofing.
When you're recording, don't make the mistake of monitoring at overly high volume levels. If your microphone is having to compete with other instruments all playing at high volume in your headphone mix, it will struggle to be heard. If the playback levels of all of the other tracks are kept in check, your microphone will have less aural competition and will appear more sensitive.
Don't assume that you must spend a lot to improve the performance of your microphone. High-end pre-amps and compressors can indeed cost thousands of dollars, but many budget models do a fine job (see Resources for examples).