Mark the highest point of the gutter 11/4 inches below the drip edge with a piece of chalk. Place marks with your chalk along the surface, moving the mark 1/2 inch lower than the previous mark every 10 feet so that water will flow to the downspout.
Find the rafter tails behind the fascia. Place a mark on every other rafter where the rafter tails are located. Drill a 1/2-inch-diameter hole through the fascia and into the rafter tail at each marking. Screw the fascia brackets into these marks with a 1/4-inch lag screw making sure that at least 2 inches goes into the rafter.
Cut your gutter to the appropriate length, remembering that most gutters that go around corners connect at a 45-degree angle. If you need to overlap two gutters to get the appropriate length of a run, overlap them by 8 inches and connect them using a 3/8-inch-long, steel screw or pop rivets.
Place rounded edges to each of the ends of the gutter that will not be going around corners or connected to a downspout. Secure the edges to the gutter by overlapping them by 5 inches and using pop rivets to tightly secure the edge in place.
Cut downspout holes. Use the end of one of the downspouts to draw an outline on the lowest portion of you runs. Use a saw to cut out the outlet so that you can install your downspouts.
Slip the gutters into the brackets along the fascia. Position the gutters so that the back edge lays slightly behind your drip edge. Secure the gutters to the brackets using a 1-inch-long, steel machine screw and flanged nut.
Use a 3-inch-wide strip of aluminum to cover the joints of your gutter and use pop rivets to pull it tightly in place. Fold the ends of the aluminum strips under the gutter to ensure you do not cut yourself when cleaning or repairing your gutters.
Connect your downspouts to the areas that you previously cut out. Secure them in place using your pop rivets and make sure that they are flush with your gutters. Add a small section of gutter to the downspout where you wish to place the final drain.