If you’re recording into a good microphone but it sounds bad, there may be a few things you can do to remedy this. For one, when recording vocals, it’s necessary to have a pop filter to reduce the sound of plosives and fricatives (“P” or “F” sounds). Some performance microphones, such as the Shure SM58, have internal pop filters, whereas many studio microphones require one to be externally mounted.
An internal shock mount can protect against noise that comes from handling the microphone. These are more necessary in live mics or radio broadcast mics than in studio mics, simply due to how much they will be handled, but are always an asset nonetheless.
Self-noise refers to the amount of low-level hiss produced by the mic when there’s no sound entering it. It’s an unfortunate consequence of the internal electrical components creating random noise that is recorded as a low, but irritating static sound. You’ll want it to be as low as possible so your vocals sound crystal clear.