I don't have much time to study, so would you tell me what it is that I need to do the most at my current level?
こんにちは。
ご質問ありがとうございます。
"I don't have much time to study,"＝「勉強に取れる時間があまりありません、」
"so would you tell me what it is that I need to do the most at my current level?"＝「なので、今の私のレベルで一番しなければいけないことは何か教えてくれますか？」
ご参考までに。
What do you think is the most important thing for someone at my level to do if they want to improve their English?
この場合、次のような言い方ができますよ。
ーWhat do you think is the most important thing for someone at my level to do if they want to improve their English?
「私のレベルの人が英語を上達させたいなら何をするのが一番重要だと思いますか？」
to improve one's English で「英語を上達させる」
ご参考まで！
アメリカ合衆国 
カナダ 
