It's mainly just my lower body and back that stiffens up, so that's where I focus my stretching. I also usually only stretch post-workout. I've read that it can be dangerous to do static stretches without warming up first and I'm usually too impatient to warm up and stretch.
Here is my standard post-workout stretch routine (I hold all stretches for a count of 30 and do each once on each leg, unless otherwise noted):
- Standing hamstring stretch: I do this three times on each leg because I have runner's knee and it is supposed to help with that.
- Quadriceps stretch: Same here; this stretch is also supposed to be good for runner's knee so I do it three times on each leg.
- Calf Stretch: I usually just do this one on each leg, unless my calves feel especially tight, then I might do it once or twice extra on each leg.
- Figure Four: I do this on the ballet bar along the wall (I usually stand on a step to do it, because I'm just a little bit short for the bar).
- Seated Hamstring Stretch: I do this on each leg once with my foot flexed and once with my foot pointed. I also do it with both legs together, again once with feet flexed and once with feet pointed. I can really feel the stretch in my lower back when I do it with my legs together.
- Seated Lower Back/Hip Stretch
If my back feels particularly tight, I throw in a kneeling back stretch
(extended child's pose in yoga).
On days when I run outdoors, which is particularly hard on my lower body, I add the following stretches:
This routine works quite well for me. If I don't do it, I definitely experience back pain or leg pain later in the day. But when I do it, I have a lot fewer issues with pain.
For kick-boxing, you should definitely be doing some sort of warm-up before hand, maybe a fast walk or a light jog for 5 min or other light cardio exercises. Once you do that, you could also do some stretches to prepare for the workout.