Ginseng comes in root and powder form, in tincture and in tablets, or encapsulated.
Most research studies suggest a standardized extract of Panax ginseng in a dosage of 200mg per day.The dry root can be chewed and a dosage of 0.5 to 2 g is suggested on a short term basis.Ginseng can also be taken in tea form, at this amount, but it is said to be very low in ginsenosides.Capsules are usually given in divided doses at 100 to 600 mg per day.If taking casules make sure they are standardized to ginsenoside content.You want at least five percent.Ginseng is usually taken for long periods.Some sources suggest a two week rest from ginseng every two to three weeks.This may depend on the health and temperament of the person taking it, as Chinese medicine looks at each individual.
If taking a tincture, take half a teaspoon in a little warm water three times a day for at least a month or two then stop for a week or two and try again if wished. 
As a general rule, acute ailments are treated for 1-30 days, although something such as influenza if it is caught early enough may only require a one or two day approach.For those illnesses which have persisted for a long time (chronic diseases) the treatment needs to be combined with healthy strategies, such as changes in diet, exercise and lowering stress.Most chronic ailments, such as an autoimmune or degenerative disease, can be brought under control when a high dosage is followed with a treatment of approximately three months.If the client cannot tolerate the herb and a lower dose needs to be used then this increases the time of recovery. Sometimes, herbs need to be taken for an indefinite period, especially if there is irreversible damage which cannot be entirely reversed, or where ailments have been left a very long time without being effectively treated.Some remedies from China are labeled with only the herbal ingredients and yet they have western drugs within them. The ingredients may be in Chinese and so it is important to be aware of this if dealing with imported products.