Every physie girl aims to do high kicks in front, but there are a couple of important things to watch out for and the way you stretch is the key!
Start lying on your back and raise your right leg, holding onto your ankle or calf, wherever you can reach, with both legs straight.  Let your right leg fall out wide, past your right shoulder.  This should make it easier.  Then, with the small of your back pressed into the floor, slowly pull your right leg across to above your left shoulder. This is a lot harder. Use your left hand to pull your right leg across your body. This will stretch different parts of your hamstring, down the outside of your leg and your glutes. Try to keep your shoulders on the floor, your neck relaxed and make sure your left leg is straight.

 
    Right leg pulled wide                                                                                                              Right leg pulled across

When you do a front kick standing up, the right leg should be in front of the right shoulder. Or in other words, your right foot is in line with your right hip, which makes the leg perfectly vertical. If you only ever stretch with your leg wide, you won’t be able to kick vertically. Remember to do the left leg too!

                      
Pulled wide, shown from above.                               Pulled across, from above