The panels should face south (in the Northern Hemisphere). The optimal tilt angle depends on your latitude. Books and articles on solar energy often give the advice that the tilt should be equal to your latitude, plus 15 degrees in winter, or minus 15 degrees in summer.
If you wanna get more technical and precise, "south" from your compass should be adjusted for the magnetic declination. This corrects for the difference between solar south and magnetic south. In the U.S. this adjustment can be as much as 15 degrees.
See
http://www.ngdc.noaa.gov/seg/geomag/declination.shtml Frank
