it's all in your legs, feet, and hands. weight transfer will determine how fast you stop and how easy it is to hold the skid.
the skids that people tell you to do with your nuts on the stem are pointless except for show. they don't slow you down much at all.
to actually use a skid to stop to slow you down you need your weight back by your seat and you're gonna have to use lots of leg muscle to stop the wheel.

you want both legs bent a little like an aggressive sporting type stance...
you use your back foot to keep the pedal from rotating forward, push forward on your bars some to help get more power into your back foot and pull up on the strap with your front foot. don't worry about trying to hold this for a long distance. it doesn't matter. just hold it for a second or two and then relax your legs, the pedals will bring your feet around and you can do the same thing in a half pedal rotation with the other foot forward or you can wait a full rotation do it again with the same foot forward. as you get stronger you can hold the skid longer and stop faster. once again, your weight is still mainly on the back wheel. remember to use your hands to push on your bars, it will help. your front and back feet should work together to almost act like you are trying to pedal in reverse.