if your fuselage is the boxy type then rounding off the corners is highly recommended as Kenliko mentioned. There is very little aerodynamic benefit from a circular to a squarish crossection. Basically your "wetted" area is bigger with the squarish fuse than the circular one. A cowling can help you or break you if its poorly designed and creates more parasitic drag. Air should flow from the front of the cowling and exit somewhere on the sides to avoid a stagnation point at the front end.
Although you havent mentioned the wings here, a little swept back on them can be beneficial too. Keep the size of the vertical and horizontal stab to the minimum allow to maintain controllable flight and if you could incorporate a V-tail instead of conventional even better, less wetted surface.