Proper immersion in the Mikvah requires that each part of the body comes into contact with the water.  As an individual descends the steps of the Mikvah, and is completely immersed in the water, the fulfillment of the mitzvah is complete. This principal is reflected in the laws that require an individual to avoid any kind of barrier that might prevent complete contact with the water.

Guidelines:

EVEN IF ALL OF THE ABOVE WAS DONE AT HOME, IN THE MIKVAH ONE MUST:

DO NOT DRY YOURSELF AFTER THE SHOWER, JUST WRAP THE TOWEL AROUND YOURSELF AND PUT ON THE SLIPPERS (SO THAT NOTHING STICKS TO YOUR SOLES) AND LET THE MIKVAH ATTENDANT KNOW THAT YOU ARE READY