Ice is the ingredient people think about least and notice most. It chills the drink, dilutes it a little, and decides how fast that happens.
Bigger melts slower
Large cubes have less surface area for their size, so they melt more slowly and keep a drink cold without watering it down. For drinks you sip slowly, such as an Old Fashioned, one large cube is better than a handful of small ones.
Crushed for the long ones
Drinks like a Mojito work best over crushed ice, which chills quickly and carries the mint and lime through the glass.
Always use fresh ice
Ice that has already been used for shaking or stirring is partly melted and will water the drink down. Shake or stir with one batch, then strain over fresh ice.
Keep it clean
Ice absorbs smells from the freezer. Store it covered, and use ice made from good-tasting water.
Enjoy responsibly.