Problem with settings?

I try to give my photos a pro-touch by using low iso and trying to expose the picture properly but i don't get pro-quality Pictures, i shoot on raw but still don't get those kind of results, My camera: Nikon D3100, Lens: 55-200mm VR Added (1). I attached one of my photos for an example

Low ISO is not a pro-touch. ISO is one aspect of the exposure triangle. By using a low ISO, you are forcing your shutter to open longer and/or your lens to open longer, to get enough light to hit the sensor. This can produce blur (shutter speed) or end up with a poor depth of field (aperture).

The pro tip here would be to not shoot a boring scene. The sky is OK, but the buildings in front are uninteresting.

If you are shooting raw, you are almost certain to be needing some post processing sharpening in any case.

That particular scene is contrasty - so although the sky is exposed ok, the buildings are underexposed - you would need to exposure blend or HDR to get the proper exposure throughout the scene.

Also, your supplied info differs from the EXIF data in the image, which quotes an ISO of 200 and a shutter speed of 1/100 sec.

The photo doesn't look good because it's boring. The buildings spoil it.

It has nothing to do with your ISO settings. It also looks like your color balance is off - it's too blue.

Photographers use the ISO they need to get the shot. ISO, aperture, and shutter speed are adjusted by photographers to get the correct exposure.

To get a good sharp photo of the sky, put your camera in Aperture priority mode, and set the aperture between f/8 to f/16 (no higher), ISO to 200 or 400 will probably do just fine. You will probably need to use a tripod at sunset or dusk. If you shoot RAW, and process in your image editing software, you can adjust the white balance to take away that bluish hue.

You have an extreme difference in brightness. Sky is partially lit by sun, so it's very bright. Back of the building is in shadow, so it's very dark.
Your camera, your printer, and your monitor can't display that wide of a brightness range correctly. That's why you have that image.
There are few things can do. If I were doing this and someone is paying big bucks to do it, I'll find a way to light that building. Multiple studio strobes placed statistically will do it. If not, I'd increase the exposure by 2 stops (do you know what this means?). Then, go to image software, like Nikon ViewNX (that your camera came with), then use highlight protection and shadow protection to recover as much brightest part and darkest part as possible. THEN, use contrast and saturation (bump them up) to cover for the loss of contrast and color.
All in all, you have a very difficult situation. I don't blame you for having this problem.
OK, since I'm sick today and bored, I took your image and corrected it in my Capture NX. I recovered your shadow, boosted contrast, and added more saturation. Is this what you are looking for? By the way, I don't see any problem with sharpness. Looks fine.