I take a scale. just any scale, a different one evryday, and play it slow, medium, and very fast. Then in thirds, and sixths. Then third each hand seperate, and sixths. then double octaves. Contray motion, and imporivise in that key. For as long as it takes till I'm happy, and feeling warmed up. Then I'll practice chopon etudes for about an hour, but I dunno whether to class the chopin as practicing rather than warming up.