One mistake I used to make very early on when I was getting readings was giving the reader too much info. And yes, I would find that they would base the readings after a while on what they already knew. Lady P was infamous for this.
I don't get readings anywhere nearly as much as I used to, but when I do, I don't tell them anything! Just "what do you see happening with me and so and so". IF they get something on their own and ask me to clarify, I will go ahead and do it, but for the most part, I tell them nothing.
Had a reader on Purple Ocean (after I submitted my order) message me and ask me several questions, and I felt she was fishing, so I didn't answer all of them aside from how long I've known him. So I figured it was going to be a BS reading but when she did the reading, she did pick up on specific things and explained her reasons for the questions..she was actually quite good. Of course, outcome remains to be seen lol.