A sheet metal shear (vs. shears) is hand-down the best way to cut PCB material - clean edge, no dust. An old-style lever-action paper cutter (not the rotary type) can also work if the board size is not too big. Sheet metal shears also work, but they generally leave marks and impart a curl to the material. The best shears are the big, ugly tin snips rather than the "aviation style" shears.