Hi Prissy,
There are a number of books on essays but I will suggest you not to confine yourself to a book only. Please make researches on a selected topic from various resources like google, youtube, newspapers, articles, etc. Some essay topics are current affairs. I consider studying "The Dawn" newspaper on daily basis.
However, you can consult these books as well.
A Professor's Guide to Writing Essays,
College Essay Essentials
The Only Grammar Book You'll Ever Need
The Art of the Personal Essay etc.
Thanks
Best Regards