A blue denim shirt and blue skinny jeans paired together are the ideal ensemble for those who love casually cool combos. And if you wish to easily up the ante of this getup with a pair of shoes, why not introduce a pair of brown suede casual boots to the equation? This is one of those season-appropriate getups that you can totally wear on your venture out into the cold. And if we're talking casual dressing ideas for men in their 30s, this combo is perfect.