Fasting will lower your metabolism which will slow the rate your body detoxifies itself. Regular exercise and a healthy diet will increase your metabolism and flush your system the fastest.

You don't want to burn fat cells near testing time (1 week) because the metabolites in the fat tissue(where thc metabolites are stored) are released into the bloodstream and will end up in your urine. It's better to eat big and be lazy during the week before a test.

On the day of the test empty your bladder before giving a sample. Peeing first into the toilet and giving a midstream sample is another tip.

Good luck