Translation:It is easy for me to read this book.
I think you mean "case", not "tense". Every noun phrase has a case.
What's a "noun phrase", you ask? Basically it's a single noun or pronoun, along with all the adjectives and articles that go along with it. So for example: "me", "the book", "that big ugly green house".
(By the way, there's also something called a prepositional phrase, which is basically a preposition plus a noun phrase: "under the wooden table". If you have a prepositional phrase, the preposition tells you which case to use for the noun phrase.)
You are right about "es" -- nominative because it's the subject.
You are right about "für mich" -- accusative because "für" always makes the noun phrase accusative.
"Dieses Buch" is the object of "zu lesen" -- it's the thing I'm reading. So, it's accusative.