Always be attentive to the quality of an herbal preparation. The herbs should be either wildcrafted or organically grown by a company of repute. A company should be willing to share quality control information with you as a customer. If they are not open with you about how they select their material, don't use their product! Many companies that package herbal remedies are not directly involved in the production of their herbs, but they should be able to tell you who they are purchasing from.
Some herbs are better as a tea (infusion), extracted in water (decoction), others are better in a tincture (extracted and preserved with alcohol). If you want to use a capsule or tablet form, make sure that you actually get enough herb in a capsule or tablet: herbal formulas with a tiny bit of 30 herbs are just not very likely to be effective, frankly. Take into account what you are using the herb for; a bitter will not work as well if you don't taste it! Your ND should be able to advise you which form is best.