Things You'll Need
Blinds with screws and support brackets
Some larger horizontal blinds, usually blinds more than 48 inches wide, are prone to sagging over a long period of time. This can be prevented by installing a center support bracket to hold the blinds in the middle. Often, if a pair of blinds is large enough to be at high-risk for sagging, the manufacturer will send a center support bracket with the product so you know when you need to use it. Sometimes the manufacturers sell center support brackets separately, so read the packaging on larger blinds carefully.
Remove the blinds from the packaging. Hold the blinds up to the window near the top where you plan to make the installation. Notice that each outside mount for the bracket is designed with holes on nearly every side, allowing you to screw the mounts to a window sill, wall or even ceiling.
Determine the placement of the blinds, whether to attach them to the interior or exterior of a window sill, to the wall above the window or the ceiling. Level the blinds, then mark the wall or window where the outside mounts will be attached.
Measure the width of the blinds, then divide the width of the blinds by two to determine the center of the blinds. Mark the window or wall in the center between the two outside mounts. This shows the location of the center support bracket.
Choose an outside mount and hold it up to the location you marked on the wall, at one end of the blinds. Notice there is a removable door on the mount. This door allows you to slide the blinds into the mount. Then it secures the blinds in the mount once the blinds are in place. Position the mount so the removable door will allow you to slide the blinds into and out of place when it is removed. Usually the door will be placed facing outward into the room. Once the mount is in position, remove the door and mark the wall where you can see the wall through the holes in the mount.
Drill a pilot hole in each hole location you marked on the wall.
Screw the outside mount to the wall by inserting the screws through the holes in the mount and into the holes you drilled.
Repeat Steps 4 through 6, to attach the second outside mount to the wall.
Insert the blinds into the outside mounts. Mark the wall in the location where you plan to install the center bracket. Indicate the top and bottom of the bracket now that the blinds are inside the mounts. You already marked the location on the wall once in Step 3; now this will show the vertical position of the center bracket.
Hold the center bracket up in the location you marked in Step 8. Mark the wall through the holes in the center bracket.
Drill pilot holes in the location of the marks you made in Step 9, then screw the center bracket into the holes you drilled.
Insert the blinds into the outside mounts and the center support bracket. Install the removable doors into the outside mounts.
Instead of installing one set of larger blinds, consider installing several smaller blinds. Smaller blinds weigh less, making them easier for some to raise and lower and less prone to sagging.