Such must-haves as a navy denim shirt and black jeans are an easy way to infuse effortless cool into your day-to-day off-duty lineup. Slip into brown leather derby shoes to instantly switch up the outfit. This look isn't a hard one to score and it's season-appropriate, which is most important when it's baking hot outside. As a 30-something Millennial gentleman, you want to start dressing more professionally. In this case, ensembles like this come in very handy.