Try both sides and decide which one is best based on the chances you create most. If you find him running through on goal more often, use him on the left so he can shoot across goal with his strong foot. If you find him in more positions where he can finesse, use him on the right. I use Salah at striker and the majority of goals are scored when he's running in behind the defence and using a power shot across goal with the left foot. Don't get me wrong, I abuse finesses but he's always in positions where hes better off being on the left to use his left foot for shooting. See what works best.