This laid-back combination of a white crew-neck t-shirt and charcoal jeans is extremely easy to throw together in no time, helping you look sharp and ready for anything without spending a ton of time searching through your closet. A great pair of dark green leather sandals is an effective way to bring a hint of stylish casualness to your ensemble. Those who are curious how to wear cool casual dressing in your early 20s, you have your answer.