If you're not a contest prep bodybuilder, I'd say yes, diet is the biggest part. Get a clean, tight diet and get it dialed in for at least 4 weeks. As far as cardio is concerned, I prefer the dumbell or barbell complexes over any kind of long distance running or treadmill work. HIIT style workouts are also great. Basically stuff where you work hard for a short period of time (1 min or less) and then rest for 30-60 seconds. As you get better, you can increase the work time and decrease the rest. Just make sure you're going 90% or better on the work.