I have often heard people say that they have a hard time getting their characters to do what they want them to do. There are a lot of people that have different writing techniques, so the advise that you might be given on how to correct this situation can be many and varied. Being that I am not a plotter but rather a person that waits on a muse, I can only say that I can never write a character until I really get to know them.
This may be the part where some would say I hear voices in my head or a good example of how writers are slightly left of normal, but when I am developing a character, I make sure to take time to get to know my character. Alicia, from this series, for example. It took me two years to really get to know her. I got to know her habits. I got to know that she likes to smoke cigarettes but only because they wont kill her, that she likes to sleep nude (mostly for shock value should she happen upon an unsuspecting person knocking on her door), that her motorcycle is like her child, that she was a detective when she was human. I get to know my characters about as well as you would know your best friend. If you give yourself time to know them, then they will do what they do without