Single leg X sweep...very fast, very effective.
Develop your guard game but make sure you have a few sweeps that you can hit no matter what. When I was a purple belt, I obsessed about sweeps and being able to get to the top position anytime in the fight. Single leg X in my opinion once developed, is one of the best ways to achieve this goal.
When performing the Single Leg X Sweep it's all about proper foot placement and shifting the hips.
When setting up the Single Leg X Sweep you want to close the distance with your opponent and get underneath them. Once you are under them it becomes a much easier game of disrupting balance and setting control of the position.
Let's focus on controlling the Single Leg position prior to the transition. By controlling your opponent in this position using balance displacement they will open the door for the perfect transition.