I frequently see its and it's misused in manuscripts. Keeping them straight is very easy.
It's with an apostrophe is the contraction for it is. If you can substitute it is, it's is correct
Its means belonging to it (Possessive pronouns have no apostrophe).
Example: I will observe the cat while it's drinking its milk from its bowl.
The first one is the only one for which you can substitute it is. You can corrrectly say it is drinking, but it is drinking it is milk from it is bowl sounds strange.
As you can see, keeping these two troublemakers straight is very easy.