I know this is an old post, but for anyone out there that has the same question maybe I can answer it.
My current boyfriend is uncircumsized and though it may be weird at first if you aren't used to it, you will end up being indifferent about the fact quite soon. From my experience the best way to stimulate him is by pulling the skin back with your mouth and sucking on the more sensitive area. Also, flickering your tongue against the tip seems to work quite well.
Other than that it is just like giving head to a guy with a circumsized penis. Take your time and vary your techniques. Suck on the sides like a popsicle, vary the speed, pay attention to the commonly ignored balls, both with your hands and your mouth, both licking and sucking them. If you are not keen on the balls instead of using your mouth you can use your hands while you are sucking by tracing around them and giving them gentle to firm squeezes and tugs. Just make sure that you are careful not to be too rough and avoid teeth. Another tip is to use your hands at the same time that you are sucking him, especially if he is well equiped in the area.
All in all, an uncircumsized penis is just as wonderful as a circumsized one and for the first time can just take getting used to and learning what pleases him!