Make sure you rest well whenever you get a chance.
ーMake sure you rest well whenever you get a chance.
「休める時にゆっくり休んでね」
make sure で「必ずする・確実にする」
rest well で「ゆっくり休む・しっかり休む」
get a chance で「機会を得る」
例：
I'm sure you don't get enough sleep now that you're so busy taking care of your new baby, but make sure you rest well whenever you get a chance.
「新生児のお世話で忙しくて、寝不足だと思うけど、休める時にゆっくり休んでね。」
not get enough sleep で「十分な睡眠を得ない」
take care of your new baby で「新しい赤ちゃんの世話をする」
ご参考まで！
After giving birth, parents tend to get short on their sleep. I'm sure that looking after your baby is hard work, but make sure to get some rest when you can.
ご質問ありがとうございます。
"After giving birth,"＝「出産後、」
"parents tend to get short on their sleep."＝「両親は睡眠不足になりがちです。」
"I'm sure that looking after your baby is hard work,"＝「赤ん坊の世話をするのは大変だと思います」
"but make sure to get some rest when you can."＝「でも、休めるときには休んでください。」
ご参考までに。
カナダ 
アメリカ合衆国 
