Place one of your shelves against the wall at the location where you'll be installing the twin track shelving. Make a pencil mark on the wall at each end of the shelf. Put the shelf down and out of the way.
Place a shelving track against the wall, 6 inches in from the outer edge of the right mark. Place a level vertically against the track to ensure that it's plumb. Mark the location of the mounting screw holes in the track onto the wall. Repeat with the second track, measuring in from the left mark. Remove the tracks.
Drill holes in the wall at each of the marks. Place hollow wall anchors into the holes. Place the tracks on the walls and line the mounting holes up with the hollow wall anchors. Insert screws through the tracks and into the anchors. Tighten with a screwdriver.
Snap the twin track brackets into the tracks at the desired heights. Lay the shelves onto the brackets.