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A nice set. You've used the surroundings to add some good interest to the shots.
A couple of quick and obvious points from me. First, all but the last 2 are very underexposed, and even the last 2 could be brightened up. The simple thing to remember when considering your exposure is to just go by the face of your subject. It's not realistic to have perfect exposure for every shot straight from the camera (although as your experience grows your exposures straight from the camera will improve significantly, but even the pros don't always get exposure bang on), and so the beauty of post processing comes into play. Just play with them sliders my friend and tweak until your subjects face is properly exposed.
Second point. Check your compositions. They are all very central which creates a boring viewing experience. The best and most effective place to start is using the rule of thirds. Place your subjects body or face onto 1/3rd of the frame and this will instantly improve the composition. Quite often you can crop later on to achieve this but in most of your images above they are just far too central to crop onto thirds.
For me the best image is number 1. The hand rails make for great lead in lines which keep pulling the viewers eyes to your subject. A shallower DoF would have made this even more effective and for me this is the only image where being central in composition works. Bump up the exposure and it will be a pleasing portrait. To critique this image further I would say that the 'danger' tape and the pillar coming out of his head is a little distracting so next time always think about what else is sharing the frame with your subject and how it affects them.