So to get down to the nitty gritty of it all, someone recently asked me on twitter what my process is for warming up. Any court reporting, CART, or captioning student or professional should warm up before a practice session on the steno machine or for speed tests. What I typically warm up with is the fingerspelled alphabet, numbers 1-100, pangrams such as "the quick brown fox jumped over the lazy dog," and then I usually jump in to the audio I was working on last from the day before, slowed down a little bit to start with.
Warming up is essential to prevent forearm muscle strain, like an athlete or musician starting slowly with stretches, and also to get the mind in sync with your fingers before starting on speedbuilding practice. Jumping into a too-fast dictation right away can sometimes be frustrating when you're not writing as fast as you thought you could, and this can lead to the steno blues.
A few months back, I posted a poll on this blog to find out what the magic length of time was for warming up for steno practice. I was pretty surprised to learn that the length of time people practiced was pretty much equally divided amongst all of the options I posted (0-10 minutes, 11-20 minutes, 21-30 minutes, 31-45 minutes, 45+ minutes, or something like that.). So there's no one right answer, in conclusion.
Experiment a little bit to find out what's the right length of warm-up time for you. Try erring on the shorter side before a round of speed tests so you don't tire out in the middle of the test, but don't skimp on the time either. When warming up before a practice session, you could probably err on the longer side. Any excess warm up can also be considered as accuracy practice before jumping into mind-blowing speedbuilding. Happy practicing, steno people!