Lay your cover material out flat on your working surface, right side down.
Place open sketchbook on top of cover material.
Draw lines 1 1/2 inches from the edge of the existing cover and cut out the new cover material along those lines.
Fold the cover material up where the spine of the sketchbook will lie inside the cover. Measure the width of the spine and make a clip in the cover material on each side and at both ends of the spine. This will allow you to pull the edges of the cover to the inside front cover of the sketchbook.
Wrap the top and bottom edges of the sketchbook cover to the inside of the front and back, and close the sketchbook to chec the position of your clips. If the inside portion of the cover material puckers or draws up, you may need to widen the space between your clips. Do not worry about making multiple clips to get the spacing right. Just fold the clipped area down into the inside of the cover behind the spine.
Flatten out your sketchbook cover material, and trace the actual edges of the sketchbook lightly on the inside.
Draw a 45-degree angle across each corner about 1/4-inch outside the corner tracing. Trim off the cover material along this line so that the material will fold around the sketchbook corners nicely.
Remove the sketchbook and, with the center spine clips folded in, place the bookbinding tape or cloth tape facing up, behind the sketchbook cover along the spine of the sketchbook. Leave about 2 inches of the tape sticking up at the top and bottom. Affix the tape to the sketchbook cover material on the side that is still facing the table, covering the spine area and then overlapping to the inside of the sketchbook cover at the top and bottom. This adds to the strength of your cover. Do not tape down the side flaps. You are only taping down the center clipped area so that the spine is reinforced.
Spread a thin layer of glue over the sketchbook's outside front cover. Starting with the clipped corners, adhere the edge of the sketchbook to the cover rubbing gently to ensure good adhesion. Spread glue over the outside back cover and start at the clipped corners again, smoothing the back of the cover in place.
Open the sketchbook and smooth glue over the remaining three back cover flaps. Roll each flap up onto the inside back cover, smoothing them out as you glue them down. Repeat for the front cover flaps.
Measure and cut scrapbook paper to fit inside the cover and over the existing endpaper of the sketchbook. Coat the inside cover with a thin layer of glue and affix the endpaper over the inside of the front cover and over the existing endpaper or first page of your sketch book. Repeat with the back cover, also gluing the ends of the elastic at top and bottom of back cover and under the endpaper. The elastic should fit smoothly around the back cover with both ends hidden behind the endpaper. Glue securely.
Cut out a pocket for the inside cover if desired. The pocket should be slightly smaller than the inside cover and should have 3 tabs extending from it. Each tab should be the length its side and 1/2 inch wide. Fold each tab in half lengthwise. Glue the outer half of each tab to the endpaper inside the sketchbook. Place the pocket so that the opening is facing the spine of the sketchbook. This will prevent your pencils from falling out. Add another pocket if you wish. Pockets work best on soft-cover sketchbooks.
Add buttons, stitching and any other desired decorations to the cover of your sketchbook.