There are a number of audio mastering tips that will help you prepare your mixes before working with a cd mastering studio. It's important to know how to prepare and submit you mixes' so you can get the best sound for your songs. The mastering engineer wants to start with a clean slate, primarily on the master bus and will need to have the proper file type and format to get the most from your music.
As you go through your mix eliminate any noise or pops that may be in each track. Use fades as necessary to cut out any spots that may just be containing recorded noise. If this is done in the mix stage within each track it will keep the overall noise level down when the mastering engineer begins to equalize and compresses the mix.
Overusing processors especially dynamic processors (compressors) on the master bus can destroy a mix and make it difficult, if not impossible for the mastering engineer to make a great master. Unless there's a specific sound of a master bus processor desired for the mix, it's best to keep the master buss free of outboard processing or plugins. If master bus processing is used make sure to notify the mastering engineer of its type and settings.
The loudest part in a mix should peak at no more that -3db on the master bus.
There should never be a limiter set on the master bus. Final dynamic control and level should be left to the mastering engineer. This allows the engineer to create the proper dynamic level for radio play, CD, or mp3 duplication.
Submitting any previously done mixes or masters of the song/s to be worked on, along with a few different reference songs that have a similar sound desired is excellent for giving the mastering engineer an idea of your musical vision. This could be a reference to bands who inspire you, or who have a similar sound you like.
Mastering from stems is becoming a more common practice. This is where the mix is consolidated into a number of stereo stems (subgroups) to be submitted individually. For example you might have different tracks for Drums, Bass, Keys, Guitars, Vocal, and Background Vocal's. This gives the mastering engineer excellent control over the mix and master, allowing for the absolute best sound possible. However, it's a substantially more involved process. If a mix from stems is desired, following the same steps listed above is best for each stem.
Note: When submitting stems, each file must start at the same time in the song even if each of the stems' audio regions start at different times.