Use these simple and effective transisions when your opponent does...
Beach Pose - Try's to Hip Escape and recover their full guard. Find the timing to switch your base and block their knee from coming through.

Around the Clock - Go around the clock when your opponent gets an underhook and attemps to get on his knees. Go around to keep his back on the ground or attemp to take his back if exposed.

Knee on the Belly - As soon as you pass the guard, you cant go wrong with knee on belly position to secure the dominant position.