Most guys like the feel and freedom of going shirtless, but some might feel self-conscious or out of place. To enjoy life without the shirt, you have to feel comfortable in your own skin. You don't need to be a bodybuilder, but you should be in enough decent physical shape if you're out in public. You also should adopt good grooming habits if you're going to reveal your body in public. The most important thing to keep in mind is that there's a time and a place for going shirtless, so use discretion.
If you do not look good shirtless, shape up before enjoying the freedom. You don't need to be a Greek god, but a decent physique is necessary. If you like the way you look, others probably will too.
Start out being comfortable by yourself. Sleep shirtless. Do homework shirtless. Become used to going around the house shirtless when nobody is home. Once you are comfortable with this, you are ready for the next step.
Venture out within your own comfortable surroundings but in front of family or friends. Take "baby steps" if you need to. You can come out of the bathroom after a shower shirtless. Leave your room in the morning shirtless. This will help build up your confidence.
Now it is time to go public. Find excuses to be seen shirtless in front of others just for a few moments, like when you walk out onto your balcony or go to the neighborhood pool or beach. Get the paper or go to the mailbox shirtless. Mow the lawn shirtless.
Take care not to go shirtless where it would be inappropriate. Be shirtless every chance you get, but do not offend others or come across as unprofessional.