Ok most important stretches are Hamstring and Groin. I u watch Cro Cops training video u will see that he basically does 2 stretches exercises after he warms up. (identical to the stretches we do at my dojo)
The first is sitting on floor and spread your legs apart as far as possible without it hurting too much......This Stretches the Groins. (remember if it hurts then dont go further this is how u injur yourself, When u have developed awsome flexability and u are well warmed up then u can start pushing some of your stretches but do not under any circumstances push past the hurt zone if your new)
In the same position lean forward and try to get your elbows to the floor...if u cant get them to the floor its ok u just need more flexability.
In the same position lean to the right andtry to touch your toes and get your head to your knee. (note all stretches u do dont bounce unless u got super flexabilty and hold the stretch for at last 10 secs and also always warm up first to prevent injury.) Repeat on the left side. Then go back to the middel and try to go a touch deeper on your stretch.( again be carful not to go to far if it hurts pull back abit and dont push through it.)
This stretch that u just did is the total package stretch i like to call it. It stretches the groins Hammys the gluts and lower back.
Then do some individual hamstring stretches.
These are the most important stretches for kicking.
Of cource there are many more stretches that will benefit u as well and the more stretches u do the more muscle groups become flexible the better off u are.
U will be told never to bounce your stretches....this is true b/c bouncing can cause injurys like strains and muscle tears.
However once u have very good flexabilty and have been training for a while u can start pulsing your stretches. This is a gentle SLOW bounce to try to get the muscles to open up alittle more. If u are new do NOT do this.
I know i am going to cop abit of flak for the last part b/c the genral rule is dont bounce under any circumstances but if u doubt my words look at Cro Cops stretching routine and e bounces big time to loosen up his muscles and he has THE best high kick in MMA.
In my dojo we also bounce very slowly once we are warmed up but always gentley never with force as this will cause injury even in the best of us.
PS sorry for the spelling and gramma errors
I hope u find some of this usful.