The biggest mistake new hikers make isn't a gear mistake - it's a trail mistake. Picking a route that's too long, too steep, or too remote for a first outing is the fastest way to turn an exciting new hobby into a one-time bad memory. The right first trail is one that lets you focus on enjoying the outdoors, not surviving it.
Trail difficulty ratings (easy, moderate, strenuous) are a starting point, but elevation gain matters more than distance for how hard a hike actually feels. A flat 5-mile trail is far easier than a hilly 2-mile one. Start with something rated easy to moderate, and check the total elevation gain before committing to distance.
Once you've done a few easy trails comfortably, working up to longer or steeper routes becomes a natural progression rather than a guess. The goal for trail one is simple: finish it wanting to do another.