If you're planning to use external flash or a reflector for fill, it may be in your best interest to start getting your friends to assist you on photo shoots. I personally hate shooting without an assistant as I prefer to have a white reflector whenever possible. As far as placement goes for the reflector it really depends on the effect you want, but for the most part I position a white reflector from below to reflect light up into the eye sockets and generally make sure that it's creating additional catch-lights in the bottom of the eye balls. The result looks like this:
Those catch-lights are important; they give life to the eyes and bring out detail in the iris. You can manipulate the shape of the catch lights as well if you're using a collapsible reflector by bending it. I like the look of square catch-lights though, so I picked up a cheap piece of white foam display board at Walmart for $2, and it works perfectly.
As for critique, I like your lighting in both photos; you do a nice job using the light to sculpt the model's features and give the image more dimension. I do agree that some fill light would bring in some more detail to important areas on both of these, particularly the hair as tirediron pointed out. Did you lose detail in the hair after editing it, or was it from your light? If it was editing, I would suggest going back in and bringing some detail back to the hair by reducing the intensity of your black tones. The awkward posing in the first shot would cause me to cut that one from the final edits. The body positioning creates a clunky rectangle in the image composition, and the right arm (camera left) positioning makes him look a bit like he has a gimpy arm with no upper segment to it; just barely raising his elbow up and a bit to the side would fix that arm issue, and having him separate his left elbow (camera right) from the side of his body so that there is a separation between the elbow and his torso would break up the clunky rectangular shape . When you're posing anyone, you want to consider the shapes that you're creating with the arms and body. Triangular shapes are particularly flattering for men, so try making adjustments in the posing that break up the body and create shapes to enhance your composition. Having your model stand square to the camera with his arms down to his side and no separation between the arms and body usually doesn't work for anyone. Even having him simply stick his elbows out just a little bit can make a huge difference. Here's another example: