you can do it one of two ways.
1) upload beyond 1080p video, at which youtube allows streaming of the original file
2) recognize youtube transcodes with avisynth and x264. by using x264 to encode your videos, it can be tweaked so that youtube's copy of x264 looses very little on its transcoding pass
it also depends greatly on the video content in question:
play havok with video codecs. especially motion. the less motion, the better.9
just on the video end for a minimum on great quality you want to upload
doing so can make a large difference at the target bitrates youtube will shoot for
the last little key is not using crap software & codecs. if you're using anything less than an h264 video codec. you're giving away a lot of quality. (this means you, WMM people using the world's worst video codec in the last 15 years...)