What you wear also contributes greatly to your personality. What you wear reflects your inner personality and is indirectly related to how you think.
You must choose your attire according to the situation you are about to face. For example, if you are going to conduct a seminar, you must look formal and refrain from the t-shirts and jeans. Whereas if you are just going for some programming stuff at any place, formal wear wont be a good decision to jump on. Programmers usually represent themselves with polo t-shirts and jeans. So wear according to the situation, the work, and the environment.
One main thing about attire is how you carry anything that you wear. If you are wearing a casual shirt and jeans without any proper way, thinking it will give you a decent look, you are mistaken. But how you carry it on you, what pair of colors you choose, whether you must put your shirt in or not is the thing you must think upon.