在五年级下册英语第二单元的作文中，学生们通常会接触到与该单元主题相关的内容。这个单元往往围绕着一些日常生活场景、人物描述、活动安排或者兴趣爱好等常见话题展开，旨在让学生学会运用所学的英语知识来表达自己的想法和描述相关事物。通过这样的写作练习，学生不仅能够巩固课堂上学到的单词、短语和句型，还能提高自己的英语综合运用能力，包括语法的正确使用、词汇的丰富性以及语句的连贯性等。

文章大纲如下：对单元主题进行简要介绍，引出要写的主要内容；接着详细描述相关的人物或场景；然后讲述与之相关的活动或事件；最后总结并表达自己的感受或想法。

以“我的好朋友”为例，假设这是本单元的一个写作主题。开头可以先点明主题：“I have a good friend. Let me tell you something about him/her.” 然后开始描述好朋友的外貌特征，如：“He/She has big eyes, a small nose and a round face. His/Her hair is short and black. He/She always wears a red T-shirt and blue pants.” 这样通过对外貌的描述，让读者对这个朋友有一个初步的印象。

进一步介绍好朋友的性格特点和爱好。比如：“He/She is very kind and helpful. When I have some problems, he/she always helps me solve them. He/She likes reading books and playing football. We often play football together after school.” 通过这些细节，使人物形象更加丰满立体。

再描述一下和朋友一起经历的一些有趣的事情，如：“Last Sunday, we went to the park. There were many beautiful flowers and trees. We ran and played games there. It was a very happy day.” 这样的情节描写可以增添文章的趣味性。

在文章的结尾部分，可以总结自己对这个好朋友的感情，例如：“I'm very glad to have such a good friend. He/She makes my life more interesting. I hope our friendship will last forever.” 这种情感的抒发可以让文章更具感染力。

如果是关于“我的家庭”这一主题，同样先介绍家庭的成员构成：“There are four people in my family. They are my father, my mother, my sister and me.” 然后分别描述每个家庭成员的特点和职业等。如：“My father is tall and strong. He is a doctor and he works very hard. My mother is beautiful and kind. She is a teacher and she teaches English.” 对于姐姐和自己，也可以进行相应的描述。

接着写家庭的一些活动，比如周末一起去野餐：“Last weekend, we went to have a picnic in the countryside. We took a lot of food and drinks. We played games, sang songs and had a great time.” 这能展现出家庭的温馨氛围。

最后表达对家庭的热爱：“I love my family very much. We get along well with each other and support one another. My family is the most important thing in my life.” 这样一篇关于家庭的作文就完整了。无论是写朋友还是家庭，关键是要把细节描写到位，让读者能够感受到你所表达的情感和所描述的内容，从而达到练习英语写作的目的，同时也能更好地分享自己的生活和感受。