Any special way you go about this? Usually there's a 2-set chatting by themselves in the bar garden, maybe in the smoking area

I tend to just be like ''Hey guys, how's your night going?'' or something, or maybe make an observation IF anything sticks out about them, but i'm wondering if I need better material because a lot of the time i'm basically getting nothing back. Maybe ignored, maybe girls that seem a bit shocked/surprised about being approached by a stranger (UK unfortunately)