I don't like studying and I think nobody likes studying at school.( at school比in school更常见,因为school不是一个大地点,所以用at.如果是一个大地点,例如一个城市,我们说in)
However,if I don't study,I won't have a good mark.(写作时,however比but更为正式.But更偏向口语）
I must study very hard,although I don't like it.
Sometimes I want to have some fun,so I don't study hard.（中文说“有时我想玩”,但是英文却不是用Play来解释的,英语里说have fun.如果说i want to have fun,就是我想要找点乐趣,也就近乎与“玩”了）
My parents are a bit worried about me,and they always urge me,"Don't watch TV and don't go online!You must study!" (这里你也可以说they always say to me,不过我觉得Urge是“劝”,可能更有那种你想表达的意思）
I appreciate that they help me so much（thank是一个动词(有时也做名词）,所以应该是i thank...he thanks,不过即使你用了i thank them,这种表达也是几乎没人说的.有一种可以是,i thank them for helping me so much.但是我觉得thank them,听起来多多少少别扭.所以你可以用一个更高级的词,appreciate,感激.还有一个问题就是,they help me more.如果前面你有提到他们帮主你什么,你可以说more,这里只要说很多就可以了.)
They love me,I know.
I always talk to myself,(跟谁说话的时候,可以说talk to someone,talk with someone,但是talk with someone是和一个人说话,当你想表达“对自己说”的时候=talk to myself) and promise myself that i must do well.(不要前面用现代时,后面用过去时.前面说talk to myself,又说say to myself太过重复.所以换成Promise）
But I can't stick to my promise for many days or even months.
Maybe this is why I don't usually get a good mark.
（it's about why...如果你换成this is why...强调性会更强）
(写好作文的一个因素就是,一个词不要一直重复着用.你可以换换别的词.你这里用了很多的always,其实代替always的,还有often,usually,frequently等等.你可以换一换.一种意思用很多方法说,才可以避免重复）