Metronome & Click Track :
With almost all of the recording sessions involving at some point overdubbing a part against a previously recorded track it is absolutely crucial to record your tracks using a click I can't stress this enough.

The best way to use the metronome is by using a dedicated click plug in run by your software - this way you are sure the click is 100% stable and free of any drifting and is following your tempo map.
Using a dedicated plug ins and not just an audio region or loop also gives you the ability to easily change the time values of the click (from 8th to 16th notes etc.). and alter its sound to suit your choice or need.Make sure that the metronome’s sound has distinctly fast attack and short duration. Remember to leave 2 bars of count in and have the music come in at bar 3.

Recording Levels :
One of the most common pitfalls of recording digital audio is clipping and distorting your signals by driving and overloading the inputs. Unlike the analog domain were distortion can be forgiving and for some even desirable digital distortion introduces many problems: adding noise to the mix, overloading plug ins and generally reducing clarity. Once the signal goes over the limit of the recording equipment its peaks gets chopped off, leaving a signal that resembles a square wave rather then a sinus. If the clipping is severe and lasts long enough, it starts being audible and sounds like harsh unforgiving noise. If it's less severe and occurs on a shorter time length, the audio starts to deteriorate and results in sounding grainy.Unlike many types of artifacts that can occur in the recording stage digital overloading is nearly always irreparable. So when recording I strongly suggest constantly keeping an eye on the meters of your inputs. If you are recording live ensemble performances, or if you know that you won't be able to easily redo your take, keep your average levels relatively low, -6 dB or -10 dB.