The biggest thing to understand, when you are using things like water circles, witch circles, pendulums and ouija boards, is that when using these things you need to be very specific on your intent and not allow anything in the questions to be open ended.
Also, you should never ask something like 'Is there anybody in this room'. Instead the question should be more along the lines of 'Who/what is in this room'. Usually, you'll get a response from what it is you are inquiring.
Other good things to know is that it is always best to do such things in a room that has been salted, or have the activity placed in a salt circle. It's best to specifically state what it is you are looking for and what you will allow in the area that has been blocked. Most importantly, never allow yourself to be open for other entities to draw energy off of you. The best way to avoid this is to wear or place copper around your physical space.
Also, other good things to note is that it is always best to use a pendulum comprised of crystal, copper and silver. Crystals can reflect/deflect energy, silver draws and copper displaces, as well as balances.
Overall, I would suggest using a tarot deck. Tarot is a lot harder for spirits/entities to manipulate because of the fact that a tarot deck uses your energies to build it's own and because a deck of shuffled cards is a lot more randomized. You have a higher chance of getting a direct answer and if anything comes to you that is ill willed, the tarot will warn you...
But that's just my opinion on the matter.