It depends on your current routines/diet/cardio etc...
But I would suggest doing some type of circuit/HIIT training.
It's fun, gets your heart rate up, and you can customize it so you can use machines or free weights.
But as it was mentioned already, diet plays a HUGE role in fitness. If you're lazy in the kitchen, your efforts will not be rewarded,
Keep those muscles confused, and keep your nutrition happening'