I recommend listening, reading and watching a lot of German-language content. Try to find interlocutors - native speakers. Also, for me personally, some sites were useful. For example, the following: https://ifu-institut.at https://deutschkurs-sprachschule.com
There are many articles on grammar and other information here.
https://ifu-institut.at
https://deutschkurs-sprachschule.com
There are many articles on grammar and other information here.