I do harrow readings without stacking the deck. I taylor the readings to the players and the campaign to my best ability as I am giving the reading. I recommend having at least the tyrantctyrant card as it is a good card for what could happen if the WW is successful.
Funny how that happens, one gets something and they all want one : ). I am running a Harrower as a NPC in the game, and she does a reading between each book for their bonus Harrow cards (mentioned in the players guide). They are to the point that they don't want any more readings since they've been pretty dark for the future!
I did these for Curse of the Crimson Throne. Did one for every AP volume the way you're encouraged to. Never stacked the deck.
I read tarot and know how to do it well. So I was finding that the harrow deck was predicting some very interesting events. Which then happened via random events, wandering monsters, and PC-led detours from the plot. Once the cards even threatened a party member, literally called him out and promised a beating if he stayed on a particular course of action.
Don't stack the deck. The players will remember the conclusions drawn by the deck and will find ways to make it come true. And then you, as GM, look completely badass.
To the opposite, from my Ravenloft experience, I'd say assume being an evil DM, and stack the deck :)
Try to know in advance which question they will ask the gypsy.
Choose the most meaningful cards for each aspect of the reading and keep them in the desired order on your DM side, hidden from the players.
When it is time for the reading in game, set the atmosphere: lower the light, and light a few candles. You can speak with a romanian-like voice if you want ;)
Make them shuffle the remaining deck and give it back to you. Then casually put it on your board side for a moment. Ask for a Spot roll (or whatever), and use this time when the players look at their sheet to secretely add on top of the deck the cards you have prepared (or whatever scheme that works with you).
Then take the deck in hand and never again let it be hidden from the players. Announce with a mysterious voice the start of the reading : "the first card represents you (or whatever aspect you need in your reading!)", then turn the card in front of the players. Then take a quick moment to look at your book, like if you are trying to see what is the meaning of this "randomly chosen" card in your DM material. Then do the reading. Announce the next card "The next card is your fate (or whatever!)", and turn it, and so on.
If you are good at acting, you can even seem surprised by a specific card's appearance ;)
Stacked deck = much better and smooth reading for the DM, with real meaning and results tailored for your campaign and your players. Since they will believe it's random, it will have more credibility and, since you chose the cards it will be meaningful and more easily understandable.
Not to stack the deck = high risk of trouble, unless you are extremely skilled at improvisation, and willing to bend your campaign to the random result you'll have with random shuffle of the deck.
The classic reading is to put the cards in a cross, one after the other. The first card is the Focus, or the person having the reading. It is placed in the middle of the cross, the others around it. Card number two is the past - a meaningful event of the past relevent to the reading's questions. Thirs Card is now - a meaningful representation of the current situation in your campaign. Card number 4 is the future - again, a meaningful representation of an event that will hapen in the near future in your campaign. And the fifth card is the answer to the players' question.
Remember to stay a bit cryptic in your answers!
Joël
And for selecting the cards, can't help you, I have a Ravenloft tarokka deck, and not the Paizo one. And I do not have a tarot deck either.
I use a tarot App for iPhone/Android phones, and tailor it to suit the party's needs/plans.
I am not familiar with the term of stacking the deck...
...also, I played a Harrower once. Drawing random cards was fun.