What could Black have done better? The sixth move was perhaps not ideal, although it did not lead inevitably to Black's difficulties. Rather, it was symptomatic of Black not thinking through his piece development. 9...Bd6 also was not directly disastrous, but betrayed the sloppiness of Black's thinking and planning in the opening. Interestingly, it was exchanging White's Bd3 that really got Black into trouble. One of the rules in evaluating the result of a piece exchange is to ask yourself who has the better positioned/more active pieces at the end of the sequence. Clearly, White replacing the bishop on d3 with his queen leads to a major positional advantage for him, which he then uses to initiate an attack on Black's king.
The simplicity with which White conducts his attack also illustrates how development and effective piece placement can translate into a successful offensive. By move 17, for example, White has four pieces (queen, knight, bishop, rook) all with great prospects on the kingside, while Black does not have a single piece that is effective there.
In sum, this short game is an excellent illustration of 1) the perils of neglecting development, 2) the importance of evaluating piece exchanges, and 3) the benefit of having a local material superiority during an attack.