your best bet is daily rigorous exercise, drinking a lot of water/cranberry juice, and eat foods high in fiber like fruits, beans, and whole wheat products. Unfortunately I am sure you know that marijuana stays in your fat cells, so it all depends on how much percent body fat you have and how fast/slow your metabolism is. My friend is a daily smoker and has to give a urine sample once a week. He takes multivitamins, which ones i am not sure and has passed his drug test every time. He is also fairly thin at age 21 and weighs 160 lbs.
So my advice is drink a lot of water/cranberry juice (i’ve heard cranberry juice is more effective), take a multivitamin, exercise, and if you continue to smoke, cut back as much as you can