You say you want to do a perfect fan... what do you mean by that?
Are you talking pretty? Perfectly spaced? i.e. have just enough space between one card and the next so you can see the number and the suit pip?
What do YOU mean? Then we can better direct you.
If you're looking for "perfect spacing", dude, it's an issue of 1) the cards you play with (I'm not one of those people that say "finish doesn't matter" because out of the box, I know some cards fan better than others) and 2) Consistent pressure of your thumb on the pivot point of the deck where applicable.
Like a previous post I've put up this weekend, it's a feel thing. as far as perfect spacing goes, I've done a fan PERFECT with a normal thumb fan, a pressure fan, the carnahan, etc.... on accident at the beginning, and VERY RARELY, and now, on accident most of the time. Practice, knowing where to put your fingers and knowing how much pressure goes where, is key with something like this, where the goal is to get it perfect on command.
If you've got the basic handling of a few fans, I recommend you just go and practice...
On the other hand, if your definition of perfect is different...