【Going to school 】without breakfast is bad for your health.
这个句子是主系表结构, 括号内是动名词做主语.
【Go】 to bed early and 【get 】up early.
这是祈使句,所以用动词原形.
不能改成Going to bed early and get up early. 因为and是并列连词,前后谓语动词要一致!