Others may have already mentioned it above -- sure buy a tree or two and have fun, kill it, but I tell all beginners to invest in yourself first - invest a lot more in yourself than in your material! Learning bonsai is like learning a language, immersion is best:
- Expose yourself to as many bonsai as possible through pictures and in-person visits to nurseries, exhibitions, and public collections. Take the time to appreciate each tree. Think about how that trunk line came to be. Look at where the branches are located. Don't fall for pretty silhouettes, and don't go in thinking everything is beautiful. Every tree has faults. Every tree can be improved. Distinguish species and build category distinctions. A pyracantha is not expected to look like maple. An ume is not expected to look like a pine.
- Make time in your day, every day, for bonsai. Only have 30 minutes, then 30 minutes it is. When I learn a language, I try to do 15 minutes every hour at first. For bonsai, I might do two 1-hour sessions per day. How to use that hour? Browse this forum, blogs, youtube, magazines, etc.
- Find good teachers - today, we have the luxury of learning simultaneously in-person and online. Join a local club, take their courses, find a mentor, but also subscribe to online teaching (e.g Bonsai Empire, Mirai Live), read blogs (e.g. Bonsai Tonight, Michael Hagedorn), get your hands on magazines, books, etc.
- Find casual conversation partners - I have 4-5 buddies that I talk bonsai with every day. I learn something new from them every day. They also keep my spirits open. I chose to specialize in Japanese species. When they talk about North American species, I listen just the same. I like 90's kokufu aesthetics, they like Hagedorn and Ryan Neil and Walter Pall and when they talk about it I listen just the same. There is always something to learn. We trade pictures of trees every day. When I send them a picture it doesn't have to be staged like it I would for social media. We see each other's real trees. We give each other real feedback positive and negative. Nobody is shy and it's always taken the right way