Does ice guarantee a great party? Alas, no. But not having enough good ice ensures that the cocktails will be horrible. You can never have too much good ice. Why? Because ice is used in 85% of all drinks. Always have new, fresh ice in the glass. (Leftover ice in the shaker is melted, and thus no good.) Ice keeps the drink cold, and cold is key. Let us underline: never, ever let melted ice water down a drink. Use cold glasses and fill them up with as much ice as you can.
Ice can be crushed in a lint-free towel using a saucepan or a mallet. You can also crush the ice in the metal part of a shaker with a muddler.