Personally, I prefer the following:
  1. Take a cup. (I use a small plastic mug... something similar should work as well. Try not to use glass or ceramic, as it spoils the taste.)
  2. Fill it up to about 3 mm. below the rim. Then, place in freezer.
  3. Check in every ten minutes or so... You're looking for a protective coating of ice that seals the entire mouth of the cup to a thickness of about a millimeter.
  4. Remove cup from freezer.
  5. Using an index finger, tap the icy covering so it shatters in an extremely satisfying way.
  6. Drink.