Stay comfortable. This may seem simple in itself but it comes down to two words, "wear layers." The morning chill can give way to bright sun and pleasant temperatures. That heavy jacket you're wearing in the morning can become a liability in the afternoon. Three to four layers and convertible pants will add flexibility to your trek. As you get warmer you can open and shed layers. If the wind picks up but the sun is shining, you can wear your shell while removing the insulation. If things get really warm convertible pants allow you to zip off the legs, instantly turning them into shorts. What ever you do don't forget to wear a hat. It can help keep you warm in the morning and cool in the afternoon.
Hike with the weather. In the fall this goes further than the logic of don't hike during the first ice storm of the year. Some of the finest hiking can be done in the morning after a sharp, dry cold front brings in a Canadian high. The air is clean, crisp and clear. If you live in mountainous regions the haze of the summer will be gone and the visibility will be incredible.
Get an early start. Shorter days means you need to maximize every minute on the trail. Start off early, before the first light so you can start your trek in the first hour of the morning. You will be rewarded with a symphony of songbirds and bustle of wildlife activity. Remember the sun will set earlier, so don't get caught out in the dark on the trail.
Be prepared. With the fall there is change, and the change is in the weather. Make sure you are ready for the elements. Raingear as well as clothing that will protect you from the wind is essential. If you are going on an extended day hike, especially into higher altitude know the weather forecast and carry a weather radio.
Move quietly. As the leaves turn and start to fall off the thickets and tangles that hid wildlife in the forest disappear. Your stealthy movements will be rewarded with opportunities to see many animals closer than you normally would. If you live in an area where there are bears or cougars, then don't follow this advice. As a matter of fact if you are hiking in bear country during the fall you should make extra noise.
Leave the insect repellant at home. Unless you're hiking in a southern climate, most of the flying, biting, nasty insects have died off or have gone into hibernation. One could easily argue that the lack of biting insects is the single biggest benefit to hiking in the fall.
Be spontaneous. There are many advantages to having flexible plans in the fall. During the warm dry fall of 1999 enjoyable hiking could be found in many regions in the United States all the way into early December. It is quite possible to have vast sections of a park all to yourself. If the weatherman says Saturday is going to be sunny and 75, its time to grab your boots and pack. Those leaves on the lawn can wait for another day.
Don't forget the sunscreen and the sunglasses. Just because it is cooler out doesn't mean you still can't get a sunburn. Drier air and wind also batters your skin during the fall months. Clearer, cleaner air also means brighter sunlight. Lip balm is also helpful if your lips get chapped easily.
Eat some food. Nibbling food as your hiking is like slowly putting coal into a fire, it keeps the internal furnace running nice and hot. Avoid having a heavy meal before or while on the trail. If you eat a lot the blood will pool in your digestive system robbing you of body warmth.
Take a friend on their first hike. Have a friend that has been asking to go on their first hike? The fall is the perfect time to do it! No insects, tepid temperatures, no crowds, greater chance of seeing wildlife, and clear skies all add up to a great first time experience. If you are bringing someone on his or her first trek try and keep it easy with an exciting destination at the end of the trail. Have a friend you want to encourage to go on a trek with you? Why not send them a copy of this story!