So a lot of the typical PUA advice on this is not nuanced and it's mostly the same. It's based around her looks. Comments like the dress being too red.
So something me and the UMP boys do is OVERvalidate girls (almost chode-like) then all of a sudden completely stop validating. It's a very noticable strip when you go to one extreme of over validating everything she is and does to zero validation or compliments. It's also pretty hilarious to watch them go crazy and fight for some scraps of validation.

In a group setting, I like to have my back to the girl and interact with the rest of the group. That to me is the ultimate validation strip. She doesn't even exist to you anymore. I use this often. It's obviously harder to do in a one on one setting haha
Another one is validating things she is saying (and smiling, agreeing) and when she says pretty much anything (really doesn't matter what she says. She could say I like puppies) you stop smiling and go "Ah ok" and just stand there. She'll be like "what? what happened?" -- "Oh nothing! it's all good" -- Now she is in her head about what she said, where she fucked up and how she can get that validation back. She is in recovery mode.
You can even say "Ah I see. So you're one of those" all of a sudden and stop validating.
Again, also hilarious to watch. They will often fight to recover that validation. It doesn't even have to be logical. It can be about her having a red car. You can make red cars a validation strip. You don't even need to explain yourself. You can even make up completely illogical reason why red cars are so DLV. They rarely question it. Women are too emotional minded creatures to logically break it down for you and think you're a complete idiot.