At 51? Ok, short version.

Single target: Open with thunder 3(you want the dot going and this sets you up for thundercloud procs), swiftcast(optional to speed up your intro), fire 3(you want to spend as much time as possible with full stacks), diversion(optional role skill use to keep your hate lower so you dont pull aggro in groups, using lucid dreaming later on in the rotation is also an option but its position would depend on when you needed to dump hate so i dont have a spot to put it on this list), spam fire 1 until low on mana, use any firestarter procs as you get them for free fire 3s - for thundercloud procs you want to use them but its ideal if the dot has ticked a couple times before reapplying so maybe wait a spell or two, blizzard 3(switching to full ice stacks to get your mana back asap), 1 filler spell(youre timing it so that you get all your mana back) - thunder 3 is good if you havent gotten any procs for it otherwise blizzard 1 is fine, fire 3(its possible youll have to delay casting this by a second or so) and repeat from there

For multi target the breakeven point is roughly 3 mobs. Against just 1 or 2 targets this will do less damage then just focusing with the single target rotation, but with 3+ this should do better overall.

Rotation: Thunder 2(now an aoe!), fire 3(same reasoning as in the single target rotation), fire 2 fire 2 fire 2(you should have enough mana to do this 3 times), flare(your hardest hitting spell and also an aoe, but reduces you to 0 mana so you want some fire 2 fillers first), optional convert and flare(getting a second one right away at the cost of a little health and a cooldown), optional potion and flare(if you have an ether that gives you back enough mana to let you go a 3rd time with a 2nd cooldown), transpose(youre at 0 mana and under astral 3), fire 3(you cast this as soon as the server tick gives you any mana back - its long cast time will give you a second tick worth of mana to use on more offense while minimizing your downtime), fire 2, fire 2, flare, transpose and repeat from there

The rotation will change as you add more skills between 52 and 70, but this is a good place to start.