I've been bad with endurance my whole life until I did the Couch-to-5k training program. Doing a 1-mile run in school was always a nightmare for me. It's a fantastic 8 week training program that alternates between run days and rest days. It starts off with run 1min, walk 2min, run 1min, walk 2min until 30min. Then it progressively gets to longer running components. I was blown away by the human body's ability adapt to stresses of running. The first week I was dying just from running 1min, walk 2min. Then mid way through, running 10min, walking 1min became a piece of cake. I heartily recommend it if you're trying to get into cardio.