Brother, ignore the people who seem to only want to mock you. Nobody is born with the knowledge of what trends are and what works for themselves. It takes a lot of experimenting to figure that out.

To keep things simple, try classifying the clothes that you have into formals and casuals. In the beginning, when you're figuring out your style, do not mix the two sets. Match the formals with the formals and the casuals with the casuals.

In this case, the shirt looks to be more formal in nature and the jeans and the sandals are very much casual. It makes the whole outfit look out of sync. Identify where you want to go.

If you're looking for a more formal setting, go with a pair of trousers, tuck in your shirt and wear shoes instead. Add a watch, a tie if you like. If the occasion is more casual, lose the shirt. Replace it with a polo neck, or a casual shirt. Find a print that you like, or keep it solid.

The jeans are not well fitted for you. The length is a bit too much making them bunch down like that which does not look very neat. Find a local tailor and alter the length. And if you can, get jeans that are not so narrow at the bottom. Your lower body is thinner than your upper body. A tapering jeans brings that more to attention. If you want balance, try jeans which are straighter.

Sandals are a matter of function over form. If you're in a place where rain/mud is an issue, sandals are going to be a better outfit choice just because of their functionality. If that's your priority, ignore the people who are saying lose the sandals. But if you want to uplift your wardrobe, a pair of sneakers will look much better on this. You can look for a pair which is (a) sturdy and (b) easy to clean if rain/mud is an issue where you live.