They say an ounce of prevention is worth a pound of cure. what about blood and lymph cancer?

No clear data: Good question, however we don't know the impact of these things on this form of cancer. There are a few international consortiums following family cohorts with blood cancers to detect what makes some of the family members develop the disease and others not- this work may identify the environmental triggers involved.

None that we know of: For most people, there is not a lot that can be done to prevent "liquid cancers" - such as lymphoma and leukemia. We don't know of any dietary changes, for example, that reduce the risk of these cancers. It makes sense, though, to follow a healthy diet, exercise, and maintain a normal bmi to reduce risks of cancer in general.

No easy way: The causes of blood and lymph cancer are generally not known, and in the cases the cause is known, e.g. Ebv infection, there is no vaccine against this virus and it is not practical to avoid exposure to this virus. Some chemicals, e.g., benzene are associated with leukemia and avoidance of toxic chemicals is about the only prevention i can suggest.

Not preventable: In spite of what anyone may tell you, leukemia / lymphoma are not preventable diseases. Down's trisomy 21, being an ataxia-telangiectasia carrier, having taking certain chemotherapeutic agents, or having radiation exposure increase your risk. The cliche about prevention applies to infectious, lifestyle, and emotional disease.