Socially Clueless

I think one reason I don't have friends is that I am just clueless socially.

I don't know what to say to people!

For example last night saw someone I haven't seen for about 6 months and she joked baout how she had been busy expanding, as in her weight - she made a motion with her hands, like she was getting a fat belly.

How do you respond to that?

A full 12 hours later I am thinking I SHOULD have said Noooooooo you look great!! As always!

Right? I mean she did look great, and not at all like she had gained weight, so not even a lie.

But instead I said something stupid like "I don't know what to say about that"

I mean, I meant I had weight issues of my own to deal with, like she wasnt alone in these concerns. But it came out all wrong of course.

How on earth do you get better at social responses anyway??