Well, not all gyms are equipped for HIIT. Unless you want to sprint on the treadmill, make loud noise and draw everyone's attention, you are best of running slowly.
I go to a beat-up gym frequented by boxers, powerlifters and weight lifters. And yes, dead-lift, squat and brench press are the base of any workout routine. I have seen some guys do only that and they are more muscled and toned than anyone I have seen.
What you eat plays an important role. There is genetics also. Some people eat as much as they want, eat whatever they want and do not gain weight and are still able to keep their six-packs to some extent. Rice is good, just avoid eating it for dinner. Do not take too much of processed, commercial protein. You do not know their side-effects. Avoid eating too much of red meat or cheap poultry. You want to stay healthy above all. You don't want your six pack to come with a cancer.