My own personal rule of thumb when working with raw herbs is to start with a daily dose of 1000mg (1/4 leveled teaspoon or 1gram). Children (75 lbs) should start out at about 1/2 that and infants (25 lbs) would be 1/4 of that. I normally give a dosage 2-3 weeks to go into effect and then adjust up or down depending on results from there.
If the specific text your'e referencing for a herbal treatment recommends a different dosage then it's probably best to use the dosage recommended in the text, assuming the author has more experience with that particular herb's potency. The above rule is just intended as a general guideline.
Homeopathic treatments assume EXTREMELY small amounts of the active ingredient. Most of my homepathic dosages are mixed from tinctures of essential oils and are diluted at the rate of 1 drop per gallon of water and then administered using standard dosage above. In my experience with homeopathic dosages the general rule of "less is more" fully applies. If I want a greater reaction than what I'm seeing after 2-3 weeks of treatment then I DILUTE the dosage by 1/2 and then observe for effect.
Remember, with homeopathic treatments you're administering a herb/treatment that would normally invoke the OPPOSITE of what you want. For instance, if I have chronic LOW blood pressure I might start a treatment of hawthorn (normally used to treat high blood pressure) at homeopathic dilutions. The thought is that the body detects the chemical signature of the reaction and then over-compensates it's reaction, thus achieving your desired effect.
I am not a doctor, nor a medical professional of any kind. My views and practices should not be taken as medical advice, nor is it intended to be. You are responsible for your own health and your own actions, not me. Consult your medical professional before starting any treatment. If your medical professional is adverse to natural healing then that is easily resolved. Find another one.