Depending on when you do this work, the last thing I would do is the spark plugs to help give the engine some time to cool off. Don't want to do a tune up on a hot engine.
While you have the intake off for the TB cleaning, you'll be able to access the serp belt easier. So might as well throw the belt on after you clean the TB, and before you put the intake back on.
Other than saving yourself a few minutes here and there, there's no reason any of them need to be done in a specific order.