More detail would be helpful :-) (interface, mic(s), instruments, etc)..
- Make sure the mic is not too far from the instrument (around a foot is a good starting point for close-miking most acoustic instruments, closer for amps)
- Make sure the Pad (-10/-20 dB switch) on the mic is not engaged unless it has to be (audible overload)
- Make sure the input channel on the interface is set correctly for the source—mic, line, or instrument (instrument = electric guitar or bass direct input)
- Make sure the input meter(s) on the interface are up at the yellow but never in the red
- Use the Gain or Trim control on the interface to set the incoming level