Where do I start from building access lists from scratch?

I just got a new job as a network engineer. The company I'm working for had a non networking guy set up everything.

Everything seems to be segmented with VLANs. They use SVIs depending on the subnet/network.

Anyway, I am trying to segment the network for security, as the firewall has a bunch of general acls with any any in the statement.

I want to use ACLs to better segment the traffic. What is the best approach for doing this? Should I use packer tracer? Install netflow and check where the traffic is going? All suggestions welcome.