Flexibility exercises should be done <em>before</em> and <em>after</em> training. This type of exercise is best if done outside. They should last for at least 5-10 minutes, in order to <em>increase</em> blood flow to your <em>muscles</em> so you can get a good <em>stretch</em>, and then a workout of high quality.
Also, what is important is not to forget to hydrate.
