1. Always use a metal tape for measurement. 2. Always write down your measurements width*drop. 3. Take measurements in centimeters for more accuracy. 4. Measure every window, as sometimes they have a slight variation that will affect the perfect fitting of blinds. 5. Add at least 10cm to the blind width & drop if it is to be installed outside. 6. Decide the operation of the blind to be on the left or right hand side. 7. Make sure you have enough depth to mount the blind inside the frame. Minimum 8cm depth is required for the blinds with top cassette and 6cm for without cassette. A lesser depth will result in the blind protruding out of the frame. 8. Look out for protruding window handles and tiles etc.