Simply push your hips sideways. As for the drills DM alluded to...
Fence Drill (or what the NPA calls the Lean and Lift Drill): Stand with the side of your glove side shoulder facing a chain link fence and your throwing side foot about 8"-10" away from the fence. Simply lift your knee and push your hips sideways toward the fence letting the fence catch you. You can start with your normal timing for when you push your hips sideways. But then change your timing to start your hips a bit sooner. For example, if you normally don't start your hips until your knee peaks, then start your hips a little before your knee peaks.
Cross-Over Drill: Start from the stretch position. Cross your front foot over your back foot. Bend your knees as necessary to get both feet flat on the ground. Perform your delivery as normal but try to push your hips sideways a bit sooner than normal. The cross-over position will make it easier to do and will also help you lead with your front hip further into your stride.
If you start moving toward home plate when your knee is on its way down, then try moving forward when your knee peaks. If you start forward when your knee peaks, then start forward a bit before your knee peaks.