Stretching

If you go to hold a stretch, but only hold it for 10-15 seconds, then you are cutting yourself short.   Every muscle in the body has little built in safety mechanisms called muscle spindles.  Their function is to immediately activate at first sense of a stretch to minimize risk of over stretching and injury.  So holding a stretch for 10-15 seconds is only scratching the surface.  At that point muscle spindles are still activated, and even though you might feel the stretch it could be much more beneficial for you to hold it longer (30-40) seconds, to actually work on lengthening the muscle for more long term effects.

Try to hold stretching for the end of your workout.  Studies are now showing a correlation between preworkout stretching and injury during exercise.  This is most likely contributed to the fact that stretched muscles create too much laxity, especially around joints, which hinder their ability to contract safely and correctly, hence possibly causing injury.

My advice, save the holding type stretches for after the workout, these are also referred to as static stretches.  Instead, start your warmup with dynamic stretches to increase blood flow to all areas of the body.  Examples would be shoulder circles, high knee walking, and monster kicks (carefully alternating kicks out front with your legs).