First you will need to make a pendulum if you don't already have one, when I first started to use one, all I used was a plumb line, which is what builders use to find level edges. Basically all it is, is a piece of string with a weight on the end. You can use anything you wish, string, cotton, nylon etc and the same goes for the weight at the end, you can use stones, crystals, keys (cleidomancy), rings (dactylomancy) nuts and bolts as long as its heavy enough to act as a pendulum. In its simplest form all you need to do is tie a weight to one end of a piece of string. Suggested string length should be around 20 to 30 cm.
There are so many suggested ways of holding a pendulum, to be honest I don't think it matters that much, at the end of the day its what you feel is right for you, that's the best way in any psychic or spiritual development. All I do is hold the string between my finger and thumb, and at arms height and at about half arms length.
Now about which hand to use, well I have two theories on this. You can either use the hand that you don't write with, the reason for this is, lets say your like me, your left handed, so my left hand would be stronger than my right hand, so if I used my right hand I would have less conscious control over the pendulum, which is what you want.
The other theory is to do with subconscious and the right side of the brain. The subconscious is the part of the brain/mind, which deals with all the psychic phenomena and spiritual contact, and also the right side of the brain is connected to the left hand side of our body, so in this theory we use the left hand to hold the pendulum. I've experiment with both and I find this theory is the more accurate for use with a pendulum. I've done a lot of experiments in this area with hypnosis and found it to be a fact. Try both to see which is best for you. You will have and advantage if you are initially right handed because you will be using your left hand, the weaker one, plus the subconscious. You can also apply this theory to anything, whether it be choosing tarot cards, runes, automatic writing etc. Another important thing to mention is the skeptics, they will often say "Well Its the Subconscious which is moving the Pendulum" and that's correct it is the subconscious, but that's exactly what you want to happen, like I said earlier its the subconscious part of the brain/mind that deals with the psychic and spiritual communication.
Ok, now we need to establish some sort of YES and NO method to use with the pendulum. We need to program the subconscious to recognize a YES and NO response. The best way I found in doing this was to consciously start the pendulum moving (make it swing) in a clockwise motion and while you are doing this you can mentally or out loud keep repeating the word "YES" over and over. Then do the same for the NO response, but this time consciously swing the pendulum anticlockwise. You may need to do each one for about 5 minutes and leave a few minutes between each response. You can also try it the other way round too, anticlockwise for YES and clockwise for NO, again whatever works best for you.
Another method is to ask a Question that you know the answer to, like "Is my name sue" or whatever your name may be, take notice of which way pendulum is swinging and this will be your YES, then ask another Question that you know the answer to but this time make it give a NO answer, if your real name is sue, and you say "Is my name Leanne" then notice which way the pendulum is swinging, this will be you NO answer.
You may find that your YES or NO answer may swing just backward and forward and not clockwise/anticlockwise that's fine as long as you can establish a YES and NO response.
Now we'll look at learning to use the pendulum. You will need some playing cards for this, a selection of about 10 will do, as long as they're equally mixed with red and black. Next mix them up so you don't know the order and lay them out face down on a table. Take your pendulum and hold over each one in turn and ask "Is this card red" or "Is this card black" and note your answers you may not get them all correct first time, but after a few weeks you will start to see an improvement. When you get a bit more experienced you can start by asking for the colour of the card, the suit of the card and even the card it self. This is actually a very good method for developing clairvoyance, you may find after a 4 or 5 months you won't need the pendulum, you will hear or see the answer in your mind.
After a few months of using the pendulum, start by using your hand as the pendulum, hold a card face down in your right palm and hold your left hand over the card and ask, "Is this card" etc. Your hand will become the pendulum and move in either clockwise or anti-clockwise motion depending on which way you have set for the YES and NO response, this can take a little longer to get used to but it does work.
Try to use the methods above continually, everyday, for about 4 weeks. You can use the pendulum for all sorts of things from finding lost jewellery to finding out your spirit guides name. As with all psychic and spiritual things don't expect instant results over night, they can take time, but you should see some big improvements in a matter of weeks.