be a true assassin and once you get the skill behind you only use your dagger i did this one time and it is the most fun i have ever had. you have the illusion spell calm in one hand dagger in the other and you calm your enemy(if you cant avoid being detected) then sneak behind them and then slit their throat
for animals if your powerful enough you can calm them and get the sneak attack as well. however i did none of the main quest on this build so i would not recommend taking on a dragon this way because i don't think the calm spell works on them