If you're not overweight and simply want to become more athletic I personally think the most important thing to do is to find an activity you enjoy. That's something you have to discover for yourself.

For example, I can't stand working out for the sake of working out at a gym. But I do get really motivated by climbing, hiking, trail running, and skiing. Climbing builds strength and has a certain level of problem solving involved too so it's mentally stimulating. Hiking and trail running are excellent cardio and have clearly defined goals to reach a certain summit or some endpoint. And skiing is just a blast in all forms. All of that keeps me active and having fun while I'm doing it. That makes me want to do it more which allows me to set bigger objectives and then it builds on itself.