I'm always on the rob when it comes to other players..
I watch intently trying to spot 'that cool thing' they do, and observe how they do it. I will then try to replicate it in my practice time. Once I have it under my fingers, I'll try it in a band situation ( as long as it's appropriate!) and if it adds to the vibe, it stays. If it doesn't, it gets saved for personal playing time.