everyone has different rotations pretty much.
I start with Swiftcast> Ice 3> thunder> fire 3> spam Fire>
Just as an opener and is situation dependant. Dunno but casting Fire 3 or Ice 3 alone and first takes casting time, my rotation the casting is sped up and seems to work fin for me.
Also when firestarted procs for example, i cast it after 1 more fire spell
Flare while some instances i do use in single targets, i just prefer to use it for aoe