Riding on trails covered with leaves requires you to be on your game even more than any other time. These decomposing deposits are not only slippery, but rocks that you usually see and avoid, are now camouflaged just enough to knock you right off your line and right into that im-movable object next to the trail. IE TREE! Also, quick direction changes are not as easy on leaf covered trails. Staying loose and riding straight down the trail with proper body position is usually more effective than trying to pick your way around rocks that may or may not be there.

The bike should be pushed out in front of you slightly. The idea is to let the bike move around beneath you without your weight being tossed around unexpectedly.
Also, try lowering the air pressure in your tires. I've seen riders struggle on the trails with fifty pounds of air in their tires. When we reduce the air pressure it's almost like they are a completely different rider. Thirty to forty pounds is a generally accepted range depending on rider weight and conditions. Lower pressure can vastly improve your traction in slick conditions. A slightly softer/ wider contact patch will also provide a little bit more give when you plow over those unseen, fist sized rocks that are hiding right below that thick layer of leaves.
The trade off to running lower pressure is that your inner tubes may be more susceptible to pinch flats. This is why I first suggest improving your body position, IE " attack position" in addition to running lower pressures.
NOW GO GET YOUR RIDE ON!