Getting the right pair
The trails you are going to be running will determine how much cushioning and support the shoe will need. If most of your running is over nice flat trails, a shoe with minimal support and cushion could work well and keep the weight on your feet down. If the trails you're running are rough with a lot of rocks you will want a stiffer mid-sole in the shoe as well as more cushioning.
If you're running over large sections of gravel it will be best for you to get a pair of shoes with deep lugs. The deep lugs allow you to dig into the ground for the best traction. If you're running in areas with steep hills you will want a sticker shoe to grip the ground as you run.
Lacing systems in trail runners
often have a speed lacing system, which allow the runner
to quickly lace up and adjust. These laces are composed of stronger materials such as Kevlar and generally will be water repellent so you don't soak up tons of water or sweat during your run.
The pronated foot is one in which the heel bone angles inward and the arch tends to collapse. A "knock-kneed" person has overly pronated feet. This flattens the arch as the foot strikes the ground in order to absorb shock when the heel hits the ground, and to assist in balance during mid-stance. If habits develop, this action can lead to foot pain as well as knee pain, shin splints, achilles tendinitis and plantar fasciitis.
A pair of trail running shoes should fit larger in the toe box to allow for foot swelling during long runs, as well it is more comfortable on downhill
sections. The mid and heel sections of the shoe should be snug creating good support for the foot. You don't want the shoes to be too tight in these areas as hot spots on your feet may occur.
Many trail running shoes now feature waterproof breathable membranes. These are a good choice for runners
who run in rainy conditions, but they are less than ideal for runners
in dry climates. If you usually run in wet conditions a waterproof shoe will keep your feet dry and comfortable during the run. The down side is that they will not breath as well as shoes without a membrane.