How should i prepare for a drug and alcohol screening/test coming up soon?

Depends: I assume you are using drugs since you asked this question. Stop using. Depending on what test(s) they are using, and what drugs you are using, most drugs and their metabolites are out of the body in as little as 3 days. Some drugs, particularly marijuana, may stick around in fat cells for weeks or even a few months. There is no way to flush drugs out of the body, and masking it doesnt work.