("Nautintoaine" is a Finnish word, compound of the words "enjoyment", "pleasure" and "substance". These are substances that are not enjoyed - drank or eaten - due to their nutritional value; like coffee, tea, chocolate, wine, beer and other alcoholic beverages, and sweets. Tobacco and drugs are also counted as a "pleasure substance".)
2) Test as much of different varieties as one possibly can. Experiment, experiment, experiment. Try out different combinations. Try the substance during different times of the day, in combination with different situations and events, like which tea suits best for breakfast and which after a meal.
The most important thing here is that this is subjective discipline. You are the only person who knows what you like, you are the only person who knows what you think, the only person who associates the way you do, and your subjective experience of the pleasurable substance is as valid as anyone else's. The difference between an expert and a layman is experience.
(Well... you DO have to be able to smell and taste, remember flavors and so on. But your experience is not less valuable than anyone else's.)
3) Ask advice and counceling from specialists, like the staff of a specialized shop. Try what they recommend, and something you have chosen yourself and experience the differences.
4) Train your senses. Use your tongue, nose, eyes and lips, your hands, even your ears, to collect as much impact as you can. I find the sensory evaluation science interesting. You can read this article to know more about that. (It also reminds us of that there are more than 5 senses that impact our experience... Take them into account as well, and train them, too.)
5) Join a group of like-minded people. Find your tribe, and discuss with them. Learn from them.
6) Visit a place where your chosen substance is made. Learn how it is made, learn about the plants or animals where your chosen substance comes from, learn the proper, best way to prepare and enjoy your substance,
7) Try making your own. Most of these "pleasurable substances" can be made at home, like wine, cheese and tobacco. (Yes. That's the way they did it in the beginning of smoking :-D)
8) Keep a journal. Write down what you have tasted and your notes. You can collect there other people's reviews and experiences too.