To adjust the string height of the biscuit bridge, remove material from the top of the bridge saddle or insert. File the string notches, making sure they're not too deep. Typically, half of a wound string's diameter lies in it's slot, while the plain string's slots are the same depth as each string's diameter. On slide guitars, the tops of the strings should all be the same height above the fretboard, so the bar will move smoothly across the strings.
Before you attach the biscuit to the cone, be sure the cone is seated correctly in the soundwell, and that the soundwell is clean and level. The area of the cone that contacts the underside of the biscuit must be flat. Place a piece of 180-grit sandpaper on a flat surface and level the bottom of the biscuit. Once you have trued the cone, biscuit seat, and biscuit, attach the biscuit to the cone using the small wood screw. Some builders, attach the biscuit to the cone with a thin bead of glue. Elmer's white-glue works very well.