I need to bleed all of my radiators. I once heard that you are supposed to bleed the downstairs before upstairs - I am not sure which way around it is, or doesn't it matter?
You should start with the last radiator on the loop and work your way from there. Most people wont know which this is unless you installed the system yourself or have labelled them. If in doubt do as you have already said, start downstairs and work your way round and up.
If you have a combi boiler remember to keep topping up the pressure via the filling loop or you will not be able to expel all the air.
If it is a vented system with an expansion tank in the loft then it will top itself up as the air is expelled.