Always start by fixing your diet and lifestyle. Make sure your diet is free of icky stuff like gluten, trans fats, processed chemicals, colorings, soy, processed grains (any processed food, actually), processed meats. Base your diet around big, colorful salads. Eat some cooked vegetables if you want, or look into the raw food diet *(I believe either can be pretty healthy). Make sure you are getting good quality sources of protein like grass fed beef, free range chicken, salmon, etc. Eat fermented foods for probiotics. Eat sprouted foods for life force and vitality.
Do this for a long time, maybe 6 months to a year. This alone will detox you a lot. Once you get to that point you can begin fasting and cleansing with herbs.
I don't recommend jumping right into deep cleansing or detoxification programs without changing your diet first. You can, but you will suffer a LOT worse detox symptoms and the entire experience will be far less pleasant for you.