I havent been able to go as much lately due to my work schedule changing but you can hand them a tip or put it in their socks, shoes, or underwear if they have those on. I usually like to give at least $5 for tips but i still see lots of people do $1 but that seems a bit low to me. As for private dances that can be up to the dancer but id say $5 a min or $20 a song seems to be the standard and minimum id aim for though i spend more with my favorite. Just discuss prior and pay attention to how much time. It is hard to keep track of songs sometimes so i usually just set a timer on my phone and tip based on time.