Spend some time coasting while standing on your pedals without sitting on the seat. Keep your arms bent and don’t lock your knees, put your pedals at the 3 and 9 o’clock positions (horizontal). Next, experiment with shifting your body towards the rear of the bike.
You will want to be in this rear shifted standing position when you coast over obstacles or when the trail gets rough. You should be standing on your pedals with your knees bent and your seat should be between your legs. This is your primary standing position.