My Chinese studies began in 1979 as an add-on to my engineering studies. This limited the amount of time that could be committed, but I had the advantage that after the first quarter I was the only student of Chinese in the University, which meant I had a private instructor for the next five quarters. The class didn't do any written Chinese, but was instead all spoken using Pinyin, audio tapes and conversations with the instructor, who was a student from Taiwan. This made for some good basic conversation.
After college I attempted to learn reading and writing on my own, which progressed for a time, but everything got stuck since there was not enough opportunity to use the language. Then in the early 1990's, my direction changed towards Japan and the effort was left off. I largely gave up hope that there would be any further progress.
But then along came Memrise with its vocabulary drill. Suddenly there is hope again. I learned that there are now 6 levels of Chinese for the Taiwan TOCFL language exam, and a similar number for the China HSK exam. Memrise has word drill sets for each of the levels, which allowed me to find out something of where I stand. The level 1 sets are a breeze to go through, provided I don't need to accurately regurgitate the spelling for the Pinyin. For example, I confuse "dou" with "duo" and often mix up the 2nd and 3rd tone, but it seems Chinese have issues with these too. The level 2 is going quickly. Level 3 has much that is familiar, but maybe half isn't. Level 4 is mostly unfamiliar. Writing characters by hand is something that I don't want to attempt unless I am forced into retirement and get very bored.
One thing that is really useful is that there are both Traditional and Simplified character drills. My self learning was originally all on Traditional characters, but I would like to be equally proficient at both. That will take some extra work, although it seems that only about 20% of the characters are significantly different. Besides the vocabulary drill, however, I need to add in some conversation and reading. Hopefully most of the skills can be moved up to the level 5.