Pick a trail that matches your fitness: a good first hike is 3 to 6 miles with under 1,000 feet of climbing. Check the weather and sunset time the day before, tell someone your route and return time, and start early so you finish in daylight. Download an offline map, because cell service is often missing on trails.
Carry navigation, sun protection, insulation, a headlamp, first aid, a fire starter, a repair kit, extra food, extra water, and emergency shelter. Even on a short hike, these items cover the most common problems: getting lost, injury, and sudden weather. Pack them in a small pouch so you never leave them behind.
Try boots in the afternoon when feet are slightly swollen, and wear the socks you hike in. You should have a thumb's width of space in front of your toes and no heel slipping on a slope. Break new boots in on short walks before a long trip to prevent blisters.
Mountain weather can change within an hour. Dress in layers, keep a waterproof shell in your pack, and turn around if clouds build or wind rises. Get off exposed ridges during thunderstorms and avoid hiking alone in unfamiliar terrain.