How do you shake a cocktail properly?

Fill the shaker two-thirds with cubed ice, seal, and shake hard for 12 to 15 seconds with vigorous movement. Strain immediately; do not let the drink sit in the shaker after shaking.

The mechanics of a proper shake: (1) Fill the larger half of the shaker two-thirds with cubed ice — bigger cubes melt slower and dilute less. (2) Add liquid ingredients on top of the ice; this minimizes splash. (3) Seal the shaker firmly. For a Boston shaker, the smaller tin or pint glass goes on at a slight angle and seals with a sharp tap of the heel of your palm. (4) Hold with one hand at each end, ice end pointing away from you and other guests. (5) Shake vigorously — full arm extension, drink moving end-to-end through the shaker, not gentle sloshing. Aim for 12 to 15 seconds for a standard cocktail, 20 seconds if you're double-shaking with an egg white (the second 15 seconds with ice after a 10-second dry shake). The shaker should feel frost-cold on the outside when done. Open immediately (firm strike with the heel of your palm on the metal seam if it's a Boston shaker), strain, garnish. Cocktails sitting in a closed shaker over-dilute very quickly.