For stretching, I like the leg up on a mid-thigh level object and then you can move your pelvis around to hit the stretching that you desire. Free style that joint. Also, butterfly stretch works too or middle split type of stuff ifyou want to work both. Heck, pretty much any of the gymnastics stuff works.
For strengthening pistols definitely work. So does sprinting, but that works both. Really any type of leg work will hit them... but if you want to be specific you'll probaly have to get some bands or ankle weights to use if you don't want to strengthen the other one at the same time.