If you want to stay healthy, you should go to bed early(保持句意不变）

You should go to bed early in order to keep healthy;

You should go to bed early unless you don't want to stay healthy.

If you want to keep in good health, you shouldn't go to bed late.
这是根据初二水平而改写的
楼上的也对

If you want to keep healthy,you'd better sleep early.

如果你想保持健康，你应该早睡