You had ( ) exercise every day to keep healthy.

You had (better ) exercise every day to keep healthy。你最好每天锻炼来保持健康。
had better do sth. 最好做某事

You had (to ) exercise every day to keep healthy. 因为have to 是必须 的意思
整句的意思是你必须天天锻炼来保持健康

You had (better do some) exercise every day to keep healthy.

better
had better do sth. 最好做某事

You had (some ) exercise every day to keep healthy

better

You had (to ) exercise every day to keep healthy.

have to do sth. 不得不做某事


或：
You had (better) exercise every day to keep healthy.

had better do sth. 表建议“ 最好做某事”

祝你学习进步，更上一层楼！ (*^__^*)
不明白的再问哟，请及时采纳，多谢！