First, have your file and razor blade in hand. Carefully peel the griptape from its paper. Save the paper, it will be used in a later step.
Next, carefully apply the sticky side of the griptape to the top of the skateboard making sure it covers the entire deck. Once it is on, gently pat down the griptape to make sure it is completely on the deck. Now, place the paper peeled off of the grip tape in step one on top of the griptape and apply pressure on it with your hand across the whole surface in order to remove any air bubbles.
With the griptape properly applied, bend the ends of it so that it takes the form of the skateboard. Then, using the file, file the edge of the griptape following the outline of the skateboard. Make sure to hold the file at a slight angle as you apply it to the edge.
Using the razor blade, cut a slit at all four pockets of the skateboard in order to create a starting and ending point for your cut. Then, carefully follow the filed outline with the blade at a slight angle cutting the griptape. Carefully pull the excess griptape as you slowly cut out the outline. If filed correctly, griptape should cut easily in four sections; the two straight sides and the two round ends.
For the last step, use a piece of the excess griptape that was cut off and use it as a piece of sand paper. Sand down the edge of the griptape to remove any excess pieces and to give the board a clean look. Lastly, using a screwdriver poke out the 8 holes for the hardware. And that is how you grip a skateboard. I gripped mine at TechShop.