我的一些愚见都在括号里了,以供参考.
Dear Sir or Madame:
First,I want to say thank you to the staff of the library
because you've done a great job.But,still,nothing is perfect.(这里逻辑不太对啊,前面说你们做的工作很好了,这里最好是说有些方面还不甚好,而不要说没有一方面是好的)
There are some suggestions I hope you would seriously consider of.
Firstly,take advices from the readers.（这里用祈使句不是很好,可以说you'd better...）espcially the teachers.The teachers know what books the students should read and they play a crucial part in activities including teaching classes,giving lectures,and doing researchs(researches).It is crucial to know what materials and books they need.
Secondly,take advantage of the Internet.(这里也是,语气需要多注意一点)Put the book names and other informations on the Internet so everybody can search （them） online.
It would be perfect and the(这里的readers 是泛指,不要用定冠词the为好) readers would be grateful if you take my advices.
Yours,
Li Ming