Shaking is simply done with a bar shaker. About 10 shakes is all that is necessary, overdoing it is futile. However, if egg whites or creamy liquers/mixers are called for, triple the number of shakes you think is necessary. These must be well shaken to produce the desired effects. Never use makeshift shakers - two glasses, one upside down over the other, is an extremely bad idea - the rims of the glasses break and drop glass shards into the mix (not to mention they leak).