Before Your First Run

Choose a well-marked, well-traveled trail to startWhen multiple trails exist in a park, run on the one that is the most worn if trails are not well-marked, and never make your own trail in a park with existing trails.
Get proper trail shoesTrail shoes should provide sufficient grip, support, and cushioning tailored to the type of terrain you run on. A wider base and reinforced heel cup help a lot with ankle stability on uneven ground.
Break in new shoes on short, easy trails firstDon't debut them on race day or a long run; stiff new soles plus rocks equals blisters.
Learn basic trail etiquetteRun to the right side of the trail and pass on the left, and don't run down the middle. Alert people when you pass — a simple "on your left" warning will suffice.
Start with runs under an hour on gentle terrainSo you can learn how your footing and breathing change off-road before tackling anything technical.

What to Pack Every Time

Carry water, even on short runsYou can't count on refill spots once you leave pavement.
Bring a map or downloaded route if unfamiliar trailsTake a map with you in unfamiliar areas, and don't depend on your cellphone, as you may have no cellular service once on the trail.
Pack a basic first-aid item and a whistleSmall, light, and useless the one time you don't have it.
Carry a headlamp if chance of being out past duskEven if your runs are scheduled during daylight hours, carrying a headlamp is always a good idea when you leave paved paths — it's essential to find a model that doesn't bounce on your forehead as you move.
Bring an emergency shelter on longer or remote runs if longer or remote runsIf you're forced to spend an unforeseen night outside, you'll be glad you carried an emergency shelter — options range from simple heat-reflective blankets to waterproof bivies.
Layer for weather swings, not just the forecast at your carTrails often run colder, windier, or wetter than the trailhead.
Pack sun protection (hat, sunscreen, sunglasses)Any time you'll be above treeline or in open terrain for a while.

Tell someone your route and return timeLet at least one other person know where you are planning to run and when you expect to return. This is the single cheapest thing you can do to make a bad day survivable.
Check the weather and trail conditionsFlash floods, ice, and downed trees can turn a routine trail into a hazard overnight.
Know the local wildlife and what to do if you meet itMake noise on blind corners, know how to react to snakes or larger animals in your area — rules vary a lot by region, so check what applies where you're running.
Set a turnaround time or point, especially near duskDeciding this before you're tired and losing light beats deciding it in the moment.

Run to the right, pass on the left, keep it to two abreast at most when running with othersBe alert when the trail crosses roads and when running in low visibility areas, and don't assume cars on the road will stop for the trail crossing.
Avoid sudden U-turns on out-and-backs if shared trailsA sudden U-turn without warning, during an out-and-back run, is a good way to get hit by a passing cyclist.
Slow down on technical sectionsRocks, roots, and wet leaves cause most trail falls, and speed is optional, footing isn't.
Watch your footing more than the scenery on descentsSave the views for flat or uphill stretches when your eyes can wander safely.
Turn back at your planned time even if you feel greatFeeling strong at the far point of a run says nothing about how you'll feel getting back in fading light.
Drink and eat before you're desperate for eitherTrail runs run longer than planned more often than they run short.

Increase distance or technical difficulty graduallyTrail running loads ankles, knees, and hips differently than road running, and ankle injuries account for nearly 40% of all injuries sustained during trail running, with uneven terrain, rocks, and roots making ankles vulnerable to rolling and twisting.
Practice on varied terrain close to home before attempting remote or high-elevation trails
Learn basic navigation without relying on your phone if remote or backcountry trailsBatteries die, signal drops, and screens are hard to read in bright sun.
Reassess your gear list as runs get longer or more remoteA 30-minute local loop and a 3-hour ridge run don't need the same kit.