I'm shocked by how few people actively smell their espresso. Your sense of smell accounts for a huge percentage of your experience of flavour. Instead of just gulping down that shot, swirl it right under your nose - you can even "cup" your demi in your hand to trap aromatics while doing this. I find it helps a bit to close your eyes while sampling the aroma - it allows for better focusing. Take your time, think about what you smell. Exhale through your nose to focus your experience of the aroma of the coffee. Then drink some of the espresso and swirl and smell again.
You'll be amazed at how much you will learn about your espresso.
"Taste is the only morality." -- John Ruskin