Heading out on a trail instead of city pavement is appealing for many reasons. Escaping into the woods gives you a nature experience that a road run often lacks. A trail's softer surface gives your body a break, too.
Trails can take away a lot of stress from the impact you'd normally get running on harder surfaces. A trail doesn't have to be steep, rocky, or littered with fallen tree limbs to provide benefits to your mind and body. Simply finding a non-paved surface, a wood-chip-covered path or converted railway bed will allow you to ease up on your joints and enjoy your surroundings.
Start by running a fairly flat trail before moving to more challenging routes with uneven surfaces and changing inclines. You'll have to pay more attention to where you're stepping and landing as you run, especially as it relates to your ankles. To prevent tripping over roots and rocks, lift your feet and your toes slightly higher than you would if running on pavement or indoors on a treadmill. Running consistently on an uneven surface can make you stronger overall, building a host of other muscles used for balance.
Don't take to the trails in regular running shoes that are designed for the pavement and other hard surfaces. Those shoes are lighter, more flexible, and are designed to cushion your feet during repeated strikes on hard surfaces. Trail runner shoes are meant specifically for off-road use. They feature more rugged soles for good traction and enhancements like extra stability and underfoot protection.