Not to sound stupid, but is there a second (edition/part) to the german lessons? I've done the first set of 24.
Are you saying you completed the whole German course? In that case, you're done with the Duolingo course, and you should supplement your German foundation with other resources to learn vocabulary, grammar, etc.
Congrats on your finished tree!
- You will learn much more German words and more difficult sentences by using the "Strengthen" features.
Here is the link to "Best Way to Make Your Tree Turn Gold and Stay Gold"
Other ways you could improve your German:
The reverse tree, the course English for German speakers, is very useful. There you have to translate much more from English to German.
Here is the link to the Duolingo Help center for "How do I switch my Duolingo course language?"
Use the web version of Duolingo (www.duolingo.com) instead of the App. The web version works also fine on a tablet or phone, when WIFI is available.
Try to read (and write) in Duolingo's German discussion forums. There you will find the daily used words, sentences and idiom.
Apart from that
- read a newspaper article every day and try to learn its new words
- listen to podcasts, watch movies with or without subtitles
- converse with a native speaker as much as possible
- write smaller texts, upload them on http://translatihan.com/ and let them be corrected by native speakers
- more information in
"Can you give some links about German?"
Duolingo will only bring you to an A2 (maybe B1) skill level in reading/writing and A1 (maybe A2) in listening/talking.
Info about language levels:
Read from "Common reference levels".