According to the British GQ, hiking sandals are a major trend for summer 2019. And if you are one of the dudes who wants to wear this trend, here are a few ways to do so:

Yes, your hiking sandals can be fun. Or printed. To go with it I picked an extreme short shorts that is by the way another trend for summer, but you can wear any shorts you like. The same goes for your top. I suggested a henley but any t-shirt, shirt would be fine.
Extra accessories that you may or may not wear: a casual watch and a hat. Why not?

Another collarless shirt. This time the short is a little longer and in a more dressed up vibe. And yes, it is pleated. But you can wear one with no pleats as well. The hiking sandals are a little dressier but still casual.
Same accessories, just because.
And yes, you could wear a nice brown belt. But bear in mind that is perfectly okay to forget about them. Even when your shorts have belt loops.

Just adding a black leather jacket in case it gets a little cold. Global warming and all.

Here the idea is go basic with khakis and a crisp white shirt (it could be cotton or linen or mix of both), the dressier sandals version, the hat and a leather watch, that is a bit dressier than the casual watch, btw.

You can totally wear a more casual (and weird) version of the hiking sandals in black and bet on a dark grey jogger to go with it. A tee that resonates with you and a casual to watch.

And yes, you can add the same black leather jacket, if you need.

The basic straight jeans with another white shirt and hat. Of course that your shirt could be in any color you fancy. Obviously. And this basic look could be the perfect base to wear a dressier hiking sandals or a more casual and fun one.
Up to you.

How about to wear a dressier trousers, dark with both sandals: a more casual one and a dressier one? Here I am keeping the top casual with a collarless shirt and a basic tee but a crisp shirt could be your choice.

And finally a suit and a polo with your dressier hiking sandals. The watch is the leather one to keep things up. A little. And yes, the polo could be replaced by any top, even a tank top. And yes, a polo could be the top of any of the other looks above.
A very important remainder: Regardless the sandals you intend to wear bear this in mind: if you are showing your feet, nails and toes, they gotta be in a great shape, looking and smelling good. Therefore, keep your nails trimmed, with no fungus or anything else alike it, keep your toes and feet moisturizer with no cracking or anything disgusting showing up. And of course, make sure it smells good. Please. 🙏
Another very very important reminder: don’t ever, ever wear socks with yours. Please!🙏🤣