I speak French pretty well but I know there's lots more I could learn. I took the test at the beginning, but am still stuck at a low level. How can I get to my level?
Even if you get all of the questions right on the placement test, it only lets you skip 40% of your tree. After that, there's nothing for it but to just do the tree, skipping Skills where you can.
Then, you will need other sources. Duolingo only gets us to upper-beginner level. AKA, A2 of the CEFR. Here are some resources that I personally like:
Intermediate resources: Practice Makes Perfect Intermediate French- Veronique Mazet Teach Yourself Complete French- Gaelle Graham (Teaches from A1-B2)
Advanced resources: Practice Makes Perfect: Advanced French grammar- Veronique Mazet Teach Yourself: Perfect Your French- Jean-Claude Arragon
You can click the checkpoint castles and take the quizzes, and it will give you credit for the appropriate skills.
But you should be aware that Duo does not go beyond a low intermediate skill level. If you are already beyond that, you’ll find little challenge on Duo. It’s still a great community, though.
Timor mortis conturbat me. 2020-05-15
If you advance as far as possible with the checkpoint castles and would like to continue through the course, perhaps to see how advanced the course is, you can test out of all of the rest of the skills one at a time, which will mean doing just one lesson per skill. That's probably as quick as you can go through the course.
You might enjoy the "reverse course": English for French speakers. Or one of the French courses from some language other than English--from Russian, Arabic, Turkish, Italian, Dutch, German, Spanish, Portuguese or Chinese. Or a course in some other language from French--Italian, German, Spanish, Portuguese, or Esperanto.
Why not try French from Russian?
Anyway, best of luck. I hope you find something you like.