Tourniquets used to be something that were all but banned from first aid and first responders. Wartime experience has shown that properly employed, they are life savers.
There are two widely recommended tourniquets, with the C-A-T being one. This video covers application on an arm. The leg is similar but slightly different and you can get to that video and others from the same folks at the end of this video if you have time to watch.
