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You'll notice that you have "extra" grip on the edges of the deck. Grab a screwdriver, a metal file, or another blunt object, and scrape it around the sides of the board until the griptape develops a white edge. This is a way of sealing the edges of your griptape. If you do this correctly, you'll have a white outline of your deck on your grip—this outline marks out the area where you should cut away the excess grip tape on the side of your skateboard. Make sure to use long strokes instead of short, aggressive ones—otherwise, you might tear up the sides. Also be careful not to file off the polish on the edge of your board. Most boards have curved edges from sanding, so you want to trim the tape past the curve along the edge. Make long and steady cut motions for the best result. Remember to hold the blade in a slight angle towards the edge of the skateboard so you don't get a small line of grip sticking out. Use the outline of your grip for reference: you need to cut along the sides of the deck, and around the nose and tail of the board.  Make sure to keep all fingers out of the way at all times, as the razor blade can easily slip from the material. Use two hands to make it easier. You do not want it to accidentally dig into the deck of your board! Once the board is completely taped, inspect it for small air bubbles. Use a knife or a razor blade to make small incisions into the grip tape; this should release any bulging air bubbles. Smooth over the incision so that the grip tape sticks smoothly to the deck. If you don't yet have trucks on your board, use a screwdriver to poke eight holes in the griptape where the screws for the trucks will go. If you already have trucks on your board, you can wait to poke these holes until you replace the trucks, or you can poke the holes as follows:  Take a second deck of the same size with no trucks on and use it as a "guide" for where to poke the holes. Mark the spots with a pencil or poke a small hole. You can now use a razor blade to cut a hole around the screw, big enough to unscrew the trucks. Unscrew each one and put them back so it looks "cleaner". If you don't have a second board, try to guess where the holes go. Try "following" the screws and poking using a needle. If you poke the center of the deck, the needle won't go far; if you poke the screw, if will go further and you will know where the hole must go. Your first attempt might look a little butchered, so go around and trim up the ridges. Run the Stanley knife, box cutter, or razor blade around the outer edge of your skateboard to remove any extra scraps. Most of the imperfections will not be too noticeable as the deck wears over time. Take a small piece of extra grip or sandpaper and lightly rub the edges where the grip sticks to the board. This may prevent the grip from peeling off the board later. While you have the knife out, you can cut a little triangle (or another shape) between the screw-holes on one end of the board. Some skaters do this to more easily identify the nose or tail of their board. Cut out a circle or a hexagon to give your board some special looks and give it interesting riding characteristics. If you want you can use paint markers or colored sharpies to draw designs or patterns on the grip tape. Be creative!
Scrape the sides. Use a knife or a box cutter to trim off any excess tape. Flatten out air bubbles. Poke holes to screw the trucks on. Neaten up the edges. Add any last-minute stylistic touches.