Looking for advice on navigating relationships

What are some things to avoid doing or saying if youre not interested in hooking up? What are some commonly understood ways to test the waters if you're not sure the other guy is interested? What are some subtle signs that a guy is flirting? How do you respond if you are interested, what is an acceptable way to flirt back and what's too much?

Sorry if this is a common question-- just new to maintaining friendships and really looking for some guidance here.

Edit for clarification: My main goal is to know the signals well enough to come to a shared understanding sooner/decrease the chances of a misunderstanding. I am the most interested in cultivating platonic friendships with other gay men, I want to be able to pick up on if a guy is attracted to me so I can shut it down when need be.