Patch into your stereo buss compressor and insert onto your master buss. In most cases you will do this on your patch bay. If no patch bay is present you may choose to run it inline with your DAW's input and outputs.
You may also prefer to use a plug-in compressor, in which case you can instantiate it onto the master buss in your digital workstation.
I mix into the buss compressor from the onset, where it typically remains throughout the process. This is key.
The only things that are usually adjusted are the input/output gain.
Adjusting the attack and release times at the final stages of the mix will alter it beyond the initial intent,
and thus totally change the character of the mix.
I like to begin the mix by setting the compressor at 2:1 compression ratio with slow attack and auto release. I use an SSL compressor and the slowest attack time is 30 ms, which is still relatively fast. I also prefer the Auto-Release function on this unit as it responds "gracefully" to the material.
Just reducing the input threshold to accommodate the program material by say, 3db, can help glue the entire mix together.
Choosing a buss compressor is also contingent upon the sound you wish to achieve. These analog units can add a sonic thumbprint and differ from design and brand.
For instance, a Neve 33609 is going to impart a darker more sluggish vibe to the mix and is great for more organic songs, whereas an SSL can add some serious aggression to a rock or pop track. The Focusrite Red creates a more transparent sound and is incredible on hi-fi pop tracks and R n B.