Don't be the guy hiding in a baggy t-shirt at the pool this summer. Focus on the following three principles of muscle growth and you'll build a body so powerful you'll want to flaunt it.
Use Compound AND Isolation Exercises
Ever wondered why the guy who does a ton of Cable Flies and Bicep Curls three times a week has a huge chest and arms? It's because isolation movements place greater emphasis on a single muscle than do compound exercises.
The majority of your exercises should focus on compound movements: Squats, Deadlift, Bench Press and Rows. But adding a few isolation exercises like Cable Flies, Curls and Lateral Raises at the end of your session will engage those lagging muscles, any that get bypassed in compound, multi-joint movements.
Shoulders and calves (even arms for some people) respond really well to high rep isolation work.
Practical tip: In my shoulder training, I use five to six reps of heavy Military Presses as my main movement. I then add 12-15 reps of Cable Lateral Raises with lower weight to completely fatigue my deltoids at the end.
Focus on Time Under Tension (TUT)
We all know guys who push the weights up and let gravity take over on the way down. Granted, if they're moving massive amounts of weight, maintaining time-under-tension is not their goal. However, if you want to build muscle, you need to emphasize TUT.
You need to keep your muscles under tension for between 30 and 40 seconds per set. If you are doing sets of 10 reps, that translates to approximately four seconds per rep. You should be taking roughly one second on the concentric (lifting) phase and three seconds on the eccentric (letting down) phase.
Advance techniques such as drop sets, supersets and negatives are additional ways to increase TUT. Just don't use them for every set, or they might cause overtraining.
Practical tip: For the Bicep Curl, take one second to raise the weight, squeeze at the top and take two to three seconds to lower the weight.
Switch Things Up
Progressive overload constantly provides your body with a new stimulus to adapt to, sparking new muscle growth. However, just as the body adapts to the weight you lift, it can also adapt to a certain exercise, leading to a plateau. That's when switching things up will help.
Program variations are endless, but you do need to stick to a specific exercise for a certain amount of time. Program hopping is one of the biggest sins, along with curling in the squat rack.
Don't try an exercise for two weeks, think it's useless and switch to another. Instead, alternate your chest building Barbell Bench Press on Mondays with a Dumbbell or Floor Press on Thursday. This might address any weakness you have on the Bench, leading to new gains when you go back to it.
Practical tip: A variation I use when my progress stalls on the Bench Press is to switch to unilateral floor presses. This exercises provides new stimulus and improve triceps strength, which will help further gains on the Bench Press.