Measure the window within the frame. If you want to maintain window sill space when the blind is down, position the blind on the outside of the frame. Add 1 inch to the width and 5 inches to the length to allow for seams and batten pockets.
Measure two wooden battens the width of the blind, 1 inch wide and 1/2 inch deep. Sand the edges to remove any rough surfaces or splinters.
Cut two pieces of fabric using your window measurements. Use thicker fabrics for good light exclusion when the blind is down or lighter fabrics such as muslin or net for a sheer window treatment.
Place the pieces of fabric together, right sides facing, and machine-stitch three sides on a 1/2-inch seam. Leave one end free. Clip the corners and turn the the fabric right sides out. Press the fabric, making the seams neat and flat.
Turn the edges of the open end under and into the pocket by 1/2-inch and slip-stitch closed or machine-stitch along the edge. Press the seam.
Pin a pocket of 2 1/2 inches depth along each end of the fabric on the same side. Tack, then machine-stitch close to the edge of each pocket. Slide the battens into the pockets.
Insert two hooks through the fabric into the top edge of the top batten, 4 inches from each edge. On the underside of the batten, insert two eye screws through the fabric, directly under the top two screws. Insert a third eye screw on the right side, 2 inches from the edge, through the fabric.
Use the length measurement of the blind to cut two lengths of cord. One should be triple the length, and the other 3 1/2 times the length. Attach one end to each of the hooks on the top of the top batten, then bring each of them down the front, round the lower edge and up the back and thread each through its eye screw going from left to right. Feed both lengths through the third eye hook.
Insert two eye screws into the top frame where the blind will hang and slip the top two hooks through the eyes. Attach a hook to the side of the window frame, facing downward. Pull the cords until the blind is fully raised and mark the cords against the eye hook. Knot the cord and slip it under the hook.