Installing blinds is a quick, satisfying upgrade. The two things that make or break the result are measuring correctly and getting the brackets level.
Inside or outside mount
An inside mount sits within the window frame for a clean, built-in look, but needs enough frame depth and a square opening. An outside mount fits to the wall or trim above the window, hiding an out-of-square frame and blocking more light. Decide before measuring, since the measurements differ.
Measure carefully
For inside mount, measure the exact width at the top, middle, and bottom and use the narrowest, plus the height. For outside mount, measure the area you want to cover plus overlap. Precise measurements prevent blinds that bind or leave gaps.
Mount level
Mark and install the brackets level — a small error shows badly on a horizontal blind. Use the right anchors if you're not hitting studs, especially for heavier blinds. Snap or screw the headrail in, add the valance, and test the lift and tilt.