Selecting a PendulumWhile any weight will do, it is better for you to take a moment and still the mind. The pendulum acts as a focus for your subconscious. So it is good to allow your intuition to decide. If it is does not come with a string or chain then you can simply tie a string to the end. Personally I would aim for less than a foot, maybe around six or seven inches.
Cleansing and Programming your PendulumThe cleaning can be as simple as putting it in a bowl of salt for a day or so, preferrably in direct sunlight. But you can also bless it with charged salt water and/or the smoke from white sage.
As to programming it, draw a cross on a sheet of paper and below it a circle. Then holding your pendulum over the cross, clear your mind and ask what an Yes looks like. Followed by a what a No looks like. You can do this over the circle as well. In the first you may find the circle moving horizontally or vertically and in the second you should see it move clockwise or counter-clockwise.
Using the PendulumNow start out with questions you know the yes or no answers to. That way you can get a gauge for the accuracy of your new pendulum. The more you work with the better feel you will get for its particular method of revealing answers to you.
If you have anything to add by all means feel free to comment below so we can all learn.