Start with what you notice
Write the coffee name, where you drank it and whether you would choose it again. A few words are enough.
Use your own flavor words
Chocolate, citrus or toasted nuts can be useful comparisons. You do not need a formal vocabulary to describe your cup.
Compare one thing at a time
At home, keep the recipe steady and change one variable. Record the change and your impression. Over time, your journal becomes a useful record of your preferences.