Corners are tough to master for most folks, as a lot of things are happening when you enter and exit each corner. The most common mistake is to look at the corner (essentially at the ground) while you are entering, passing through, and exiting the corner. Try this: Find a corner that has a smooth arc that you can ride in second or third gear with confidence. Choose a smooth corner, one without rocks or whoops, so you can focus on technique. As you begin to enter the corner, leave your foot off the rear brake, this is not a slide into/power out of corner technique. As you enter the corner, turn your head towars the exit of the corner, keeping your eyes at the same level as before, and look past the exit. You are essentially looking at WHERE you want to GO, not where you ARE in the corner. Your head will naturally rotate back to center as you exit the corner, making you ready for the next corner/obstacle/trail tansition.
Most folks will look at the ground in front of their front tire, but the reality is that whatever is going to happen in that section of trail is going to happen whether or not you see it or not, as you are traveling too fast to compensate for that unkown obsacle anyway. Trust your instincts to compensate for whatever is in the apex of the corner, and force yourself to ride based upon where you want to go, not where you have been.
Give it a shot, I think you'll increase your corner speed, as well as your enjoyment of the trail. Think it won't work? Next time your watching your favorite National MX rider go around the track at the next National, watch his head. As he enters the corner, his head will snap to the exit, essentially making the spot where he wants to go.
Rick