Sterling is improving all the time.
His main attributes of pace and close control are very potent.
He benefits and suffers from playing with players like De Bruyne, Sane, and Silva; because their decision making (particularly De Bruyne's and Siva's) are so outstanding it sometimes pales him by comparison, and along with his patchy finishing it gives some a stick to beat him with.
However, he is learning from these players all the time, and whilst his decision making and finishing are erratic, he is still getting into the positions to make these errors which shows how excellent his positional awareness is.
He should become England's best player once it all knits together.