I did Spanish but u can revise in the same way for German ... use Memrise or Duolingo, have a vocabulary book with u with vocabulary (search for high level ones or write down from Memrise) u can use all the time
Or alternatively u can get a sheet of paper and divide it into 8 sections QACNOTTI Q for qualifiers like too much, A for adjectives, C for connectives, N for negatives like I hate, O for opinions like I love, T for tenseslike (I will do...), the other T for Time phrases like tomorrow and the I for idioms coz those will get u a higher mark....
After u learn each topic make a mind map and use wat I told u above
On a sheet of paper u can write down like phrases that’ll get u a really high mark which U can get off the internet
Learn tenses and how to conjugate coz that’ll really help
Read the revision guide watnot