What is the best way to resolve differences between state and federal laws

There really isn't much room for state laws to upset federal law. If there is some dispute, where it is not clear whether a state law is violating a federal law, the decision about that would usually meet up to a federal court to decide. As someone else wrote about marijuana for example, this is an area where the selling and possession of marijuana is a federal crime as it is listed as a schedule one drug under the controlled substances act however the federal government has decided not to involve the department of justice and have them go into the states that have decided to legalize marijuana, and start closing down and arresting the stores and facilities that are providing the drug. Technically they would have the right to do so, but everything in our government is also tempered by politics and since most Americans believe that marijuana should be legal, it would be a problem politically for the federal government to use their resources to get involved in state decisions that approved the sale and use of marijuana, hence they have decided for political reasons, despite Jeff sessions Utterly moronic position on marijuana, Not to get involved.