There are three common uses of the pronoun "it":

As an idiom

"It is snowing";

To postpone the subject

"It is untrue that a rhinoceros can run faster than my tights"; and

As a personal pronoun

"I wanted a rhinoceros for my birthday, but did not get it."

You may use all of these in academic writing, but to avoid awkwardness, you should not use more than one within a single sentence:

[WRONG] When it is my birthday, I hope to receive a rhinoceros, and I will walk it often.

It would be better to eliminate the first (idiomatic) "it":

On my birthday, I hope to receive a rhinoceros, and I will walk it often.