Ricardo De La Riva shows us how he sets up a basic DLR sweep from guard. Notice how he moves his hips outside of his opponents leg to make room for him to slide in the DLR hook. If you don't make space by moving your hips you may not be able to get the hook set properly.

It's important to get the push/pull timing down so make sure to practice plenty of reps. The DLR guard in general relies on a lot of precise positioning and timing, if you are forcing the sweep something isn't right.