From side control, the way to mount is sliding your knee across his belly. The biggest obstacle is his near leg. When it's pulled up, it closes the road and gives him half guard. So you pin it to the mat first, or wait for your chance, and only then bring your leg across.
Stay low and keep your weight on his chest. Lift your hips and go over the top, and you give him space to shrimp back to guard. The best moment is when his attention is somewhere else: he's defending his neck or has just failed an escape.