Your problem is (1. 缺少冠词 a) common one among middle school sudents．
Maybe the following advices （2. 抽象名词 advice 用了复数形式，改为 advice） can help you．
First in （3. 介词错用，应该是 of） all，believe in yourself．
Your greatest problem is that you lack（4. lack 当“缺乏”讲是不及物动词，后面应该有介词 in） self-confidence．
The first thing you must do is to smile at （5. smile at 意思是“置之一笑”，smile on 是“对...微笑”）your classmates．
One smile speaks loud（6. 后面有 than，说明是比较结构，应该用 louder） about your wish to make friends than any word．
Your smile will show that you are friendly to him （7. 呼应上文的your classmates，改为them）．
Next, trying (8. 非谓语动词用法错误。此处用祈使句表示建议。应该用 try) talking with a student or who share（9. 动词形式错误，shares） the same interest as you．
You can discuss your studies with a classmate, and you can also（10. 重复错误，后面有 as well，删除 also） talk about your hobbies as well．
Unless （11. 应该用 if）anyone is in trouble, you should be ready to help him or her．Once you have confidence．you can make as many friends as possibly (12. 不能用副词，改为形容词 possible)．
高考改错题中只有九个错误，是否这里有打错的地方。请你仔细检查以下。