1-approach the rail/box straight on, shoudler squared to the box/rail, feet a lil wider than shoulder width apart, and look towards the end of the rail
2-pop off of the lip, wait for tails to clear the lip, turn your body 90 degrees (if you arent comfortable with turning 90 at first, try turning 45 then increasing the degree more each time)
3-once on the rail, keep your feet wide, (i was taught to use the gorilla stance, where you keep your knees bent a lot and keep your stance low) i like to keep a little more weight on my downhill foot - DO NOT lean back cause your feet will slide out from under you and you will eat some shit
4-keep lookin towards the end of the rail, once at the end, pop off, turn 90, stomp the landing, and then ride it out like a homie