Beware of river flush draw slow played my 6 set and lost pot

My bad - lesson learned. I slow-played a set of 6s on the flop and built the pot but wasn't thinking about the flush draw which villain to my right collected and took the pot down with. I lost the pot because I wasn't flush draw aware. Another one I need to be aware of as well as yesterday's straight draw losses. That's why I'm practicing first and using whatever means necessary without incurring a real dollar cost.