Open the highest valve first, then run the system slowly, gravity and the water flow will push out any air. After it's bled, I check the pressure with a handheld gauge. It’s a simple way to do it, but it works well.
I've found that using a vacuum bleeder works well on cooling systems. It gets the air out quickly and keeps everything clean. As for hydraulics, I usually cycle the actuators all the way a few times to get rid of any trapped air.