Chapter 4-1-6: Use "it" consistently within a sentence
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.