Safe to say Infernal Circle should be placed down whenever possible. It has a long CD so careful positioning is a must to maximize DPS. Staying in the circle offsets the mana drain from Arcane Amplification and should be used [ideally] for T-skill bursting.
Speaking of Arcane Amplification it should be used sparingly. You can switch between Arcane Amplification and Arcane Focus quickly due to the short CD but if Infernal Circle is on not available or movement is required Arcane Focus should be your go to for mana regen.
*Note* This is taking account the ideal rotation [i.e no movement/interrupting/healing needed etc]
Fireball is your filler spell. Always Ignition after Ritual Pyre for the bonus damage. Ignition
has a shorter CD then Ritual Pyre so you can weave it in before it comes back up. After 30% weave in Incineration