You will need piece of paper that's bigger than your foot, a pencil, a butter knife, and a measuring tape (or a ruler, if it's longer than your foot).

Measure your foot later in the day, preferably in the evening.
Your foot actually expands throughout the day, the more you walk on it, and the more you're upright.

Wear a sock when you measure your foot, since you'll almost certainly be wearing socks when you wear your shoes.
Try to wear socks similar in thickness to those you will be wearing with the shoes you hope to get.

 The instep
Place a measuring tape around the instep.  
Pull the tape snugly around the foot.
Mark on the foot tracing exactly where the tape is placed.  
Record the circumference measurement.  

Send us your measurements in centimiters for both feet.
        Right - Lenght: ___ Width ____ Instep ___
        Left -    Lenght: ___ Width ____ Instep ___