Put on your golf shoes. Have a friend or a person at a golf shop measure the distance from one of your wrists to the floor with a tape measure. Make sure you're standing up straight and your arms are held straight down at your sides. Repeat with the other arm.
Measure how tall you are from the floor to the tallest part of your head. You can do this by using a doctor's scale with a height-measuring apparatus, or you can stand against a wall, mark your height and then measure from the floor to the mark with a tape measure. You must be accurate.
Find a golf-club sizing chart to reference. You can find one either on the Internet or in a golf supply shop.
Find the measurement of your wrists to the floor on the sizing chart and match it up to the measurement of your height. (Generally, most charts will list heights in inches across the top of the chart and the wrist-to-ground measurements on the side.)
Determine whether you'll need custom-made clubs. The numbers on the chart will indicate whether you can use standard-sized golf clubs or will need to have them custom-made. If your number on the chart is negative, you'll need to subtract the negative number from the length of a standard club. If it's positive, you'll need to add the positive number on the chart to a standard club.
Order or purchase your golf clubs in accordance with the information gleaned by measuring.