How can you tell that friend of girls knows me better and talk more?

[Diego]

Some of my acquaintance friend of girls said "we don't talk much". On Facebook. And others I said Hi in the hallways and talking about what we doing in school. The problem is that I don't have anything to say to them and also I don't know how to become a good friends. I don't want to lose them and also they have different classes as me but we seen each other mostly in the hallway and mostly in the field trip. Can anyone help me how to figure this out? Please be specific!
Also some of them are in my class too.

[postal p]

Maybe you can hang out with them after school. You can see what they talk about, and join in.