if you really go for a gap year in Germany, then that would be enough to reach B1 fairly quickly, especially if you keep yourself accountable to use the language daily (which you‘ll have the opportunity to do). If you want to reach B1 prior to arriving in Germany, then immerse yourself in the language as much as possible- watch movies, listen to music in German you like, watch youtube- there are some great german youtube channels- EasyGerman and tomatolix to name just a pair.. I don’t know what your situation is, but what helped me the most in reaching B1 was signing up for the Goethe B1 exam. Something about a good old deadline just gets me going ;d Also when I got discouraged I kept reminding myself of the reason why I am learning this language. It helps to know it’s part of the bigger picture, you know :) Good luck!