For a casually cool look, wear an olive plaid long sleeve shirt and navy jeans — these items work really well together. Ramp up the formality of your getup a bit by finishing with brown leather brogue boots. So when summer is done and fall is in the air, this ensemble is likely to become your go-to. Gents who wonder how to rock semi-casual dressing as you work your way through your 20s, this ensemble should answer your question.