Summarize:

Generally, the handle for the screen door should be on the same side as the handle for your main door. However, if the handles will interfere with each other or if the screen door will open and hit an object, have it open in the other direction. Even though the screen door may not be heavy to lift and hold in place, you need to have your hands free to properly secure and install it. Recruit a willing family member or friend to just gently apply pressure on the screen door so it does not fall forward. If you do not have someone who can hold the door in place, remove the door once you have confirmed it fits. It is easier to attach the hinges to the door when it is not in the door frame when you are working by yourself. Shims are thin, tapered items that are used as spacers. Place at least 1 shim along the top and bottom of the door, and 2 shims on each side. This is an easy way to double-check that there is the needed 18 inch (0.32cm) gap around the entire door. If the shims cannot be inserted, this means that portions of your door frame are not square. For minor adjustments, lightly sand the screen door if it is wood, or sand the wooden frame until it fits. If both your door and frame are not made of wood, have a professional safely square the frame and finish installing the door. The hinges will be on the opposite side of the door from the handle. Make marks along the edge of the door that are 5 inches (13cm) from the top and bottom. This is where the upper and lower hinges will be placed. The last hinge will be placed centrally to the first 2 marks. Alternatively, to avoid measuring for the hinges, align them to match the hinges on the inside door. This works best if the screen door and the inside door have the same dimensions. Use a pencil to make marks on the door so they can be easily washed off. Align the hinge with the measured marks you made on the door. This will ensure that you drill the needed holes in the proper place on the door. Drill the necessary number of pilot holes needed for each of the 3 hinges in the marked areas on the door. Slowly install the screws until the hinge is firmly pressed against the door; otherwise, you might cause the hinge to twist or fall out of place. There will most likely be 3 mounting screws per hinge, so try and start with the middle hole on the hinge to ground it, and then the outer ones. Only use the hardware that came with the screen door as those pieces will work best for hanging it. Repeat this process until all 3 hinges are properly secured to the door. With the door being held in place, use your drill to secure the hinges to the adjoining door frame. Start by making starter holes, using the attached hinges as a guide, and then install the mounting screws. Since you have already properly mounted the hinges to the door and have the door properly spaced with shims you should not have to do any measuring for this part. However, you may want to use a level to double-check that the door is still sitting evenly before screwing it in place. If you are hanging the door by yourself and applied the hinges on while the door was laying flat, you need to place the door into the door frame before finishing attaching the hinges. Open the door to double-check that the hinges aren't sagging and are properly supporting the door. This could mean that you did not fully set in the mounting screws. Then close the door to ensure that it naturally fits back into the door frame. If it seems like it is rubbing, then try loosening or tightening the mounting screws accordingly until the door fits. Since these can vary in style, follow the manufacturing instructions on how to properly install the handle components it came with. Generally, there will be starter holes on your door, but if there isn't, use the height of the handle on the interior door as a reference. Even if your knob or pull is not on the same side as the interior door handle, have it be the same height for ease of use.
Decide which direction the door will open. Have someone help you safely put the screen door in the door frame. Wedge shims between the door and the frame to check that it fits. Measure the placements for the 3 hinges along the length of the door. Use a hinge as a template on the door and drill pilot holes for the screws. Use a drill to install the mounting screws into the pilot holes. Attach the hinges to the door frame. Open and close the door to see if it needs any adjustments. Install a decorative door knob or pull to make using the door easier.