I always run the engine without the radiator cap in place to "burp" the system.
Fill the radiator with coolant, start engine and stand there with a couple of jugs of 50/50 mix, watching the coolant level. When the thermostat opens, you'll notice the level will drop severely. Pour in the coolant and just keep watching it. It will slowly stop going down and you'll get a consistant level. Then I just let it run for a bit to get any air out and then put the radiator cap back on and fill the overflow tank to its proper level.