If you're lucky enough to have a forest full of Autumnal colour you'll need a wide-angle lens while a macro lens will be handy for getting in close to one or two leaves.
A polarising filter will cut out the reflections you can get from the surface of a leaf, and if you're heading off to the woods, it's a good idea to take a tripod along for the longer exposures you'll need to use in the darker conditions. A cable or remote release will also be handy as you'll be able to set the exposure going without having to touch the camera's shutter button, minimising the chances of shake spoiling your shot. If you don't have a release but do own a Smart Phone, some cameras can now be remotely controlled by them via an app. Take a look in your camera's manual to see if it's compatible with this technology.
If you want to add backlight to a leaf but the sun's not playing ball pocket your off camera flash or if the sun is out you may need the flash on the other side to stop the leaf appearing as a silhouette.
A forest decorated in Autumnal shades is always worth a wide shot or two. If you're at ground level try and find some foreground interest to fill the space and to give the viewer something to focus/guide their eye through the rest of the photograph. A large rock, bolder or bench will contrast well against the colourful scenery. Climb out of the valley and onto the hillside and you'll have a picturesque landscape that's a patchwork of greens, reds, oranges and yellows. Try shooting a panorama if it's a particularly impressive scene.
If you can kick the bed covers off early try to head out at dawn when fog/mist will still be lingering around as a landscape of colourful trees with morning mist slowly crawling across it always looks impressive. It works particularly well if you're on a hillside looking down over a valley, but you can have just as much success down on the ground among the trees. Here you may need slightly longer exposure times, though, so make sure you have your tripod to hand.
Once you're back down off the hill, take a closer look at the leaves for shapes and patterns worth a quick snap. Clusters of leaves that have fallen on the ground are great for backgrounds while the veins of an individual leaf will give you an interesting abstract shot. If you're emphasising the patterns found in the leaves try lighting from the side or to give the autumnal colours some punch, add some backlight. You may need a little fill-in flash to stop the leaf silhouetting against the sky and use a small F number to really throw the rest of the leaves dangling on the tree out of focus.
If you have a stream or river near by, use slow shutter speeds to blur the water as it passes the leaves decorating the banks or if there are a few rocks in the river where the leaves have fallen, fill the frame with them and use the blurred water as a frame.