I know, use a lossless format, but
If I have a client, employer,potential employer who insists on being sent an example of my work on MP3. Is there a fast way to mix, knowing I have to use MP3. Are there predictable losses with Mp3 so in anticipation I can mix differently? Very interested. Thanks 



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Do not, I repeat, do not try to do anything special for mp3!

It's the lowest resolution portable format and it does what it does.
Make the best mix and master in full 24 bit quality. The mp3 made from this will sound it's best when your mix and master sounds it's best.

Do this:
24 bit mix
24 bit master (this is your full quality final product)
16/44.1 portable master
mp3

Advanced:
You can peak limit the master intended for 16 bit a little extra if you feel the level needs to come up to preserve the lower level dynamics. This is what's commonly done to accommodate the portable format. Make the mp3 from the portable master.