Hi Markus,
This is a rather good photo and I am sure your friend is already using it extensively to promote his new album. Technically the capture is good but there are a couple of things you could do to improve the image.
To begin with, I think you can tighten the tone control on this photograph. The blacks are rather muddy while his face also seems to be lacking contrast. Often people use the Auto Levels to get a picture correct but in a photo like this where you have bright lights (these are automatically creating a white point beyond the usual scope of the scene) and very dark shadows, chances are the Auto Levels will not suffice. In this instance I would open up the curves and gently nudge the white and black points inwards. You will see a difference.
Lens flare is also a problem in this photo, particularly on your friend’s hands. There is not a lot that you can do about lens flare but it is still nice to try and get rid of it. Often this can be done by gently cloning it out in Photoshop… although take your time to get it right.
Now, the final point worth mentioning is that Exit sign behind the lights. This photo could almost have been made anywhere were it not for that sign… The scale of it belies the rest of the picture. Again, clone it out if you get the chance.
It is worth noting that you can kill a lot of time Photoshopping out flare and signs from photos which is why I usually do it to the hero photos. Don’t feel compelled to go through every photo from the night and remove these faults!
Cheers, Anthony
Image Doctor's edited version