Original poster, please disregard Tao's post. I could spend an hour ripping, but instead I'll just regurgitate "Parkour is a sport/discipline/activity/art of easily accomplished movements. Nothing here takes much physical force, with the exception of very few movements," and say, "Really?"
Stretching: Movement compensation: many modern folk have pattern overload, like sitting too much. That example leads to tight hip flexors, which will cause your body to handle forces in an inefficient manner. If you still possess movement compensation, then corrective static stretching should be your main priority. Hold tension on knots for 20 seconds or so and the muscle will relax itself through autogenic inhibition.
Reciprocal inhibition: a more active stretch is prescribed after sessions of static stretching have done their job. Active isolated stretches focus on increasing range of motion of individual joints, and are accomplished by using the antagonist (muscle on the other side [quad/hammy]) to relax the muscle being stretched. Stretch out the joint by pulling on it with the antagonist, hold 1-2s, and repeat 5-10 times per muscle.
Dynamic stretching: Once you're flexibility is pretty on point, go through your body's full ROM fairly explosively for a good warmup.
Ballistic stretching: Heard it's actually great for power training if applied after autogenically inhibiting the muscle. Look this one up for yourself, I don't entirely know, but it seems right.
Exercise selection: Drills to improve balance, both stabilization and movement core musculature, ground reaction forces, and speed, agility, and quickness are just as important as resistance training. Try holding single legs extended in the sagittal, frontal, and transverse planes. Single leg squats. Single leg touchdowns. Variations on prone iso-abs, bridge, cobra, bicycles. Landing drills, step ups, box jump. Cone/line drills in sprint, shuffle, and carioca step. Advance all skills slowly in a progression that includes not just sets and reps, but adding directional challenge, proprioceptive challenge (do it on the ball, basically), and progressing from static to movement, with increasing tempo.
Resistance training: a great tool, the weight. Adding a block of whatever to an exercise for each body part will make you very strong, if done right. I recommend vertical loading, going top to bottom one body part at a time, and then repeating from the top for more sets. Stability resistance training is sort of important for parkour, as movements must be done with particular importance to balance and grace or else it becomes freerunning [joke. jk. rofl.] For this, use a lighter block of whatever, and do it in a way that challenges your balance, from single leg variations to the railing, to the wobbly railing, and one set of 12-24 reps per body part. For strength, possibly in supersets with stability, wink wink, do 8-12 reps per body part, and as far as sets go, if you're doing too many, add weight. For power, take the block and toss it. Explosive strength, wooooo pk4life. Just take that last piece of advice from the last paragraph and apply it here, too.
For a how-to for every exercise under the sun, try exrx.net.
Strength vs. Endurance: Train Stability Endurance for Strength Endurance for Power Endurance for MAX POWER. Lets look at running. A runner must be strong, smart, and go for hours if he is to run an antelope to death. A good runner is balanced, and has a great core, and is quick and powerful, because the strikes must be strong to keep the machine going, and fast to be efficient (180bpm) and you'll notice their head is erect and doesn't bobble. If you could just run easy, you can run some more. STABILITY ENDURANCE! If you could just run some more, you can run harder hills. STRENGTH ENDURANCE! If you could just run harder hills, you can run hard, anywhere. POWER ENDURANCE! Freerunning ... MAX POWER!