I think just generally knowing how the game works, especially when everybody is dealer and they have to deal the cards out. It can be difficult working out how a new player thinks.
I usually have a look around and see what's open, depending on the day/time, not all poker tables will be running. You can then decide whether to stay or go elsewhere,
In my previous job, i tested online Slot machines and I can tell you, they aren't worth it. The win percentage is very low when you take into account winning lower amounts than your stake and breaking even.
It's difficult as i generally watch the losers more than the winners! With the amounts i bet, i generally don't mind if i win or lose so it's not a big deal.