The pronoun it is unusual in that it doesn’t always need an antecedent:

It is raining.

It is warm today.

In academic writing, however, many expressions that start with it — It is well known that; It is worth noting that; It may surprise many to learn that; and so on — do no real work and should be avoided.

Do not use it in an indefinite sense:

On the foundation’s Web site, it shows a running tally of malaria deaths.

Usually with this pattern, you can find the true subject of the sentence nearby:

The foundation’s Web site shows a running tally of malaria deaths.