Riding up the slope of a trail is more fun than riding down. But whatever goes up must come down.
The best way is to stand on the foot pegs and strike a balance between your brakes and gravity. Doing this requires a decent amount of skill and a low sense of self preservation. You must be ready to ditch your motorcycle in an instant and jump away from it. Unlike when riding up a slope, you don’t have the luxury of gassing your way out of a sticky situation. You slam your brakes too hard and they will lock up good. Your motorcycle will slide down the path of least resistance, not necessarily with you still on it. Needless to say, you need to turn ABS off because you actually want your wheel to lock and free up at your command giving you an edge over gravity. You need to concentrate on the handlebar and have it point in the direction you wish to go. Let the rear wheel do whatever it wants. You have little control over it anyway.
The not so nice way way is to sit on the seat and ride down using your legs to waddle your way out of a sticky situation. This method is far more exhausting as it puts severe strain on your thigh and calf muscles and breaks your back. With my present skill set this is how I ride down slopes. I hope to upgrade my skills and degrade my sense of self preservation so that I can move to the first method.
If all else fails there is no shame in simply walking your motorcycle down the slope.