This is the stretches that have helped me most - I have my right splits and almost my left splits now.
First start in a lunge with your back knee on the ground, lean forward, but make sure your front leg stays perpendicular to the floor. Try to get your hips toward the floor. If that's easy, you can lean forward and try to put your elbows on the floor. Then slide backward until your front knee is straight(but not sitting on your back leg), and try to touch your head to your knee. You should be trying to hold these for a minimum of 30 seconds. Trying to work up to 1 min seems to be the most recommended. But remember not to push yourself to far or too fast, or you'll pull something again. It will take time. Hope this helps!