Is there any way to prevent leukemia?

Not really. Certainly one can avoid exposure to agents which promote cancer: many of which are outlined in the state of california website where many substances have to be labelled as being possible carcinogens - but other than this..Avoiding exposure to extremely high doses of radiation such as atomic bomb blasts are about the only known things you can do to lower the risk.
Not really. Exposure to benzene (a solvent in the chemical industry) can cause leukemia, but most cases of leukemia have no exposure to benzene.