The key to getting correct answers from pendulums is to be as detached as possible to the question at hand. Pendulums work partly on subtle, subliminal muscle convulsions and (in my belief) energy from the Universe. When you ask a question to such a sensitive medium, your emotions can obscure the reading. Like, if you ask, "Will I find $1,000 in the next ten minutes?" and you reaaaally want that money, the answer can come out "yes" despite it most likely being "no".
Sodalite is a good stone to have a pendulum made out of, as it promotes seeing the truth and such, but any stone will work just fine as long as you keep it cleansed**. Some people believe a spirit presides over the pendulum, and if that is your belief it wouldn't help to try meditating to bond with it. Programming it to give a little boost of energy never hurts, of course.
The more you use a pendulum the easier it becomes, and in my experience the percentage of "correct" answers improves. I put the word in quotes because I believe that the future is very, very dependent on our every little action. Once you hypothetically know the outcome to an event that has not come to pass, it puts that outcome in jeopardy.
** Not all stones need cleansing: selenite and citrine cleanse themselves.