1. Let's not rush it.
2. Let's not rush it too much.
(What is the meaning of these sentences? What does "it" refer to here?)
This phrasing means "let's not go too fast" -- whether it's about making a decision or traveling from one place to another or any other action that could result in a bad result.
"It" is just a general term, and it's reference depends on the situation in which it's used.