The first stalemating threat occurs when the enemy king sits in one of the corner squares. In this case, it is crucial not to place your queen a knight's move away from that corner!
In the diagram above, the White queen prevents the Black king from having any legal moves because it sits a knight's move away from the a8 square, on c7. It would also be stalemate if the queen were on b6.
The easiest way to avoid this stalemate is to make sure the enemy king has at least two safe squares before trapping it in a corner. For instance, if the White queen were on d7, the Black king could harmlessly shuffle back and forth between a8 and b8.
