the key to growing a green thumb is finding a plant that actually interests you. For me that plant was Cannabis. Doing my own micro grow in a 22x38x64 [cm] box forced me to learn about all sorts of things of relevance to a plant:

- light intensitiy, spectrum, sources

- fertilizers

- soil types

- watering patterns and methods

- vermins and how to deal with them

- plant physiology and developmental phases

- water quality, pH levels

also I think that it's worth starting from seed. this makes it more personal.

another interesting plant is cactus (in my case San Pedros to be specific). though, they are much less of a hassle compared to Cannabis. but that led me to asking about how cactusses anatomically relate to regular plants, needed to learn yet another watering pattern, looking forward to grafting.

vegetables are also cool. I personally don't find much interest in plants which are just standing around, serving no purpose - pretty much exactly what I'd get from those suggested in the article.