My teacher was talking 90%, but it was good to practice my listening skills.
My teacher was talking most of the time, but it was a good listening exercise for me.
ご質問ありがとうございます。
まず、「9割方先生が喋っていた」というのは
My teacher was talking 90%
My teacher was talking most of the time
と表現することができます。
そして「リスニングのよい練習になった（よかった）」
it was good to practice my listening skills.
it was a good listening exercise for me.
ご参考になれば幸いです。
日本 
