Best way to set up boundaries and enforce them in a new relationship?

1. She posts a lot of memes on social media
2. Whenever I post a girl's pic she posts a guys pic, she's petty at times
3. Limiting her talking to other boys
4. Not alot of red flags so far, she responds quickly, she reinitiates texts/convos more than I do, etc

So how do I go about setting and enforcing boundaries, early on in the relationship, it's only been 3 weeks so yeah.

Note: Don't have much experience with relationships