I like to purge my keg with CO2 before I transfer, when you open the keg, you'll see the gaseous co2 floating in there. Run you siphon tube to the bottom and cover just enough of the top of the keg to let the tubing in to keep dust and particulate from falling into the keg.
Don't forget sanitize your siphon tubing and autosiphon/racking cane before transferring. Once all my beer is in the keg, I like to take a packet of knox unflavored gelatin dissolve it in a boiled half-cup of water. I pour the solution into my keg, seal it, and stick it in my refrigerator to cold-condition for a few weeks. The gelatin will drop any of the yeast remaining in suspension nicely. Discard your first two pints or so, and the beer will run clear in less than a week.