Just like a blazer, a soft pastel blouse and a leather jacket, the denim shirt is a classic. Denim on denim is a difficult look to get right, you don't want to end up looking like you're off to a rodeo or a tacky mid-west American. The trick is to mix light denim with dark and preferably without embellishments. A dark leather belt and a bronze cuff brings it all together.
Avoid straw hats and boots. Unless you're going to a dress up jol!