Thats on live? Where its all suposed to be scaled with higher ilvl gear etc? Okey... I dont think we should worry too mutch even before full gear etc, Sure mutilate is really boring to play with 2 min cds, but if you pref sub, youll make it work.
Id say just start duel alot, even tho it might sound noobish but I think its a good way to practice. And i think dueling other rogues is a good way to improve your reflexes as its way more prediction and fast paced then other duels. + you will maybe get an understanding of what he is doing and why, talk about the duel afterwards etc.
And remember rogues are getting buffed in 5.4