1) Ideally leave -6dB's from the 0 dBFS ceiling when printing mixes to stereo.
2) Do not use any leveling tools like limiters or normalizers on the stereo bus, unless they are a vital part of the sound.
3) Never change the sample rate (kHz) of the files.
4) Print, render or bounce your tracks as 24-bit floating point data files (wav or aif), 16-bit or mp3 files are not suited for mastering!
5) Don't use any noise shaping, and dither only triangular if necessary.
Stereo mastering is the final process before a song is released to the public. This is where levels are balanced, frequencies receive finishing touches, and any other problems with the mix are ironed out. Files submitted for mastering should be in the highest resolution available, and generally in .WAV or .AIF format.
Additionally, for the best possible masters, I recommend removing any pre-mastering processing such as limiting, and keeping the highest peak-level of each song at -1dB or less. This allows me enough headroom to best sculpt the dynamics and overall sound of your songs. Finished songs are delivered as downloadable Standard WAV files. Check the following list to ensure the best result!