I spent 2 years writing 500-word warmups before every story, and the fix was 3 sentences
For a long time I figured the warmup had to be a real scene or it did not count. So every morning I sat down and cranked out a full page, then got annoyed when I had no gas left for the actual draft.
Last month a guy in my writing group in Akron asked what I was doing and said "that sounds like a draft, not a warmup." Something clicked. Now I just write 3 lines about whatever is on my desk, a mug, a receipt, whatever, and stop. Takes 4 minutes. I have finished 6 short stories since then, which is more than all of last year.
What do you all use as a warmup that stays short? I keep wanting to turn mine back into a real piece and I need a rule to stop myself.