My process is to fill the keg with Star San, force the Star San out with CO2, put a hose on a gas disconnect and hold the end of the hose directly in front of my face; turn the keg up-side-down and put the disconnect on the gas-in post to blow out the ounce or two of remaining Star San and to release the pressure. This leaves me with a keg full of CO2 at ambient pressure and a nice, clean pair of glasses.
Connect a hose from the spigot on the bottom of my primary to a liquid disconnect on the liquid-in post of the keg and open the spigot. Keep the gas disconnect on the gas-in post so the beer will flow.
If you have a lot of hop debris or other crud above the level of the primary spigot, you may need to remove the center poppets of the liquid post and the disconnect.
Once you have transferred the beer, you can blow CO2 in through the liquid-out post to get a head start on carbonating and to seal the lid.