best way mate to build up is simple run lol, warm up is best done whilst your jogging, well how i do it in the gym in the army lol, just run along shake your legs off, then swing arms around a bit look like a plum but the blood is pumping then so it works better, start of steady then just keep building yuor pace up, when you have a set route and you can run it without feeling sore that is the time to increase the distance, the last 400 meters slow down to a steady walk and as your coming in start shaking legs off, when stopped do a full stretch down from head to toe covering all the muscles. g