How do you get the tile or glass so uniformly shaped??

While looking through the posts about bowling balls and some other mosaic pieces, I noticed that everyone's tile or glass pieces are so uniformly shaped. Some are triangles, other's are squares and others are different shapes, but they always seem so uniform. I made a bowling ball with broken glass, but when smashing the glass, I had very irregular pieces. Some were just tiny slivers and others were large odd shaped pieces. Do you use a special tool? I really need some guidance, I know nothing about doing mosaics. TIA, Staci