Make a fist with both hands, then touch the sides of your hands and thumbs together like in the diagram above
Start at the left pinky knuckle - this is January. Then move to the depression to the right, just before your next knuckle - this is February.
Knuckles are 31 and depressions are 30 (or 28/29 in the case of February). Continue moving along the knuckles and depressions of both hands and matching each spot with a month of the year (as pictured above).