Well in my experience there's 2 potential opportunities involving spoilers
Companions quest line:
Spoiler When you start the quest and Vilkas or whatever his name is ordered to spar with you to test your worth, you can smash him with magic. He will just repeat saying magic isn't their way and you should use a sword. Keep in mind he could do a lot of damage to you.
And during the dark brotherhood questline:
Spoiler when you complete the story and build your torture room, you can freely practice any magic on the torture victims. Be careful not to kill them... They do not respawn.
Alternatively you could put flames/frostbite/sparks in one hand, and healing hands in the other, and spray that on easier creatures.
I've also found that the more magic cost a spell generally has, the more it will boost levels. If you can, try sneaking around dungeons with rune spells. It really helps to have the quiet casting perk for this method.
Hope it helps.