Decide what you’re training for—distance, speed, or general fitness—and pick metrics that match, like GPS distance and pace for races, heart rate for endurance, and cadence for form. Prioritize comfortable, compatible wearables with reliable GPS and continuous heart monitoring, then match battery life and features to your budget (starter, midrange, premium). Factor environment: trail needs long battery and rugged gear; road favors lightweight accuracy. Test and sync devices with apps for consistent data, and keep reading to learn specifics.