You should put away the toys you're finished with before you start playing with other ones.
You should put back the book you have finished reading before you start reading another one.
ーYou should put away the toys you're finished with before you start playing with other ones.
「他のおもちゃで遊び始める前に、遊び終わったおもちゃを片付けてね」
to put away the toys で「おもちゃを片付ける」
to start playing with ... で「…で遊び始める」
ーYou should put back the book you have finished reading before you start reading another one.
「他の本を読み始める前に、読み終わった本を片付けてね」
to put back the book で「本を片付ける」
to start reading ... で「…を読み始める」
ご参考まで!