I substitute Fireball instead of Pyroblast depending on the wow power leveling situation. If there are walkers about and the chance of interruption, I will go with the shorter fireball. If the target is a caster, I will run up slightly and insert a counterspell after the first spell and then cast mana shield and fire or frost ward then continue on with the sequence. If the target is moving, You better use fireball or that six seconds will just be wasted when you go to cast Pyroblast and they are out of range. Also remember that the damage is NOT that significantly greater with pyroblast vs. fireball on the front end but the Damage Over Time is where Pyroblast sets itself apart. I use fireblast at the end instead of Frost Nova because 1) I am trying to deliver as much dam as possible in the shortest amount of time 2) I want my fireblast to cycle as soon as possible. I find that if i use Frost Nova then Fireblast, they tend to break out of the frost nova faster so I tend to stay away from the fire instants when they are rooted in ice. Maybe its just me. Also, If one of my first two spells stuns him, I will immediately add a fireball in wherever the stun came. If the stun happens on the second fireball, I will fireblast then fireball. I will probably get hit at this point prolonging the last fireball but it will pay out dividends in the long run.

Usually fireblast is not available or quite cycled yet so I will resort to Magic Missiles to finish my opponent off as they are running or if there is no other enemy they can add, I will just run after and keep hitting with my staff or wand til fireblast comes available. Magic Missiles are great for runners because although it is not an instant, they do start delivering damage half-way through the channeling process.