Do this stuff and watch the video and practice practice practice.
1) Get your seat down and use a mid-foot position on your pedals. Cornering is all about getting your hips moving around the bike and if your seat is in the way it can be a lot tougher to do. In fact, if you try to learn with your seat up you’ll most likely pick up bad habits.
Also, you’ll need to be able to drop your heels so you can weight the outside foot and “carve” the corner which requires a more mid-foot position on the pedals. I recommend flat pedals since they naturally put you in this position but if you run clipless then make sure you don’t have the cleat set under the ball of the foot as this will throw your weight too far forward and make it harder to use your as hips effectively.
2) Be able to ride switch-foot so you can enter a corner with the outside leg to the back. This will let you drop your heel and carve the corner better by giving you a better platform to laterally hinge the hips from. Even though you can get away with either foot being forward entering a corner - and there are times you want to keep you dominate foot forward in fast paced DH sections - you will be better able to execute your technique if you can get your outside foot back. I've also found that most of the time riders who argue this point can't ride switch foot in the first place and are looking for reasons to not have to learn how but that is another subject for another article.
3) Set your hips before entering a corner by weighting the outside foot. If you enter a corner balanced it is too late, you’re going to be playing catch-up with your balance points through the corner. By shifting your weight and entering the corner with you hips set and ready to shift you can set your edge faster and more easily dictate the balance points.
4) Use counter-pressure to lean the bike over and your vision to pull you through the corner. When entering a corner you want to lean the bike over by pushing with the inside arm and look through the corner to make sure you ride smoothly through it. Counter-pressure is critical to maintaining good traction and since you go where you look your vision is your ultimate guide.
5) When all else fails focus on shifting the hips laterally and not squatting down or leaning over with the shoulders. When you are doing it right you’ll feel your ribs laying down one by one on top of your inside thigh.