基础性的语法错倒没有.主要毛病是几个句子的主、谓、宾的逻辑结构不清晰,有的关系混乱.先改了,供你参考:
In our life, we always face some accidental harms. Usually these harms may not influence our normal life. But sometime, it is very dangerous having suffered from a serious harm, even causing loss of one's life. To be sure, it is necessary that we should learn some knowledge of first aid in order to prevent us from serious harm. For example,if one's carotid is punctured by sharp objects,we should let the patient lay without moving,and use towel to wrap the wound to avoid further bleeding. Then,we should resort to the hospital. Because,in normal situation,a carotid can maintain blood for 30minutes. For other example,if one suffers from an accident,we should firstly bound his injured position,and keep the patient without moving until doctors are coming. So, mastering a right method of first aid is greatly benefitial to us.