Brake bleeding order

What is your question?

Can anyone provide me with the order that the brakes need to be bled? I'm changing the Master Cylinder this weekend on my sisters car and I want to make sure I'm bleeding them in the correct order. Also just to get another opionion on what's wrong. She said the pedal goes to the floor every now and then which I find odd that its only sometimes. She doesn't have a leak, no air in line so I would assume thats its a faulty master cylinder. If it was the brake booster it would only make it really hard to press the brakes correct? Thanks in advance for the help.