Sometimes the surface doesn't offer the amount of grip you'd like to make the corner. If you want to keep moving on loose terrain you're going to have to get loose yourself, and relax. Fighting friction and gravity will soon send your sideways drift downwards.
Entry Speed - Entry speed is important - it is the speed you'll have to deal with throughout the corner. Touching the brakes mid-drift will throw you off line and cause you front wheel to wash out. If you need to brake, feather the back only.
Body Position - Treat loose corners the same as flat corners by getting your outside foot down with as much weight as you can on the edges of your tires. Being over the top of the bike will keep you in control if your bike starts to drift.
Line Choice - The main considerations are consistency and turn. Choose a line that has a relatively consistent surface throughout the turning phase for similar levels of traction and trail feedback. Try to keep turning to a minimum on the loose stuff by setting up early and wide.
Foot-Out - On really long flat corners having your foot out not only increases confidence, but also lowers your center of gravity and allows you to lean the bike even more. You'll get more traction as the extra weight over your outside foot helps your suspension on track, but you'll really compromise exit speed.
Tip: Keep your bike leaned over but don't lean with it, this will enable you to drift without losing balance. The easiest way to practice loose corners is on a downhill fire road but avoid the classic crash caused by a loss of traction over the 'looser' center.