There are three main considerations when brewing tea: tea quality, water temperature and steeping time. Start by measuring 1 teaspoon of loose leaf tea per cup of water. Fluffier blends may require 2 - teaspoons. Next, heat your water to the temperature recommended. Use fresh water whenever possible. Water that has been sitting in your kettle overnight may impart a flat or stale taste to your tea. Finally, steep your tea for the amount of time shown below. Keep in mind that brewing your tea for too long can extract bitterness from the leaves, so steeping time matters. For a stronger tea, don't steep longer, just use more tea.
White and Green Tea - Infuse for 2-3 minutes in 180º water. If infused longer than 2-3 minutes, White and Green tea can become bitter.
Black Tea - Infuse for 5 minutes in 212 º water (boiling). If infused longer than 5 minutes Black Tea can become bitter.
Herbal - Infuse for 5-7 minutes or more in 212 º water (boiling water). Infusing Herbal tea longer than 7 minutes will NOT make it bitter, only stronger.
For White, Green and Black Tea, do not infuse it longer, add more tea leaves to your infusing ring, ball or teapot and then infuse it at the right temperature and length of time. For Herbal Tea, since herbal tea does not actually contain any "tea" leaves from a tea plant, the longer you infuse the tea, the stronger it will become.
White and Green tea can be re-infused 3-4 times, so instead of throwing away infused tea leaves, simply set them aside and re-infuse them with water for a second cup of tea.
Black tea can be infused a second time with some loss of flavor. Adding a pinch of fresh tea to the used leaves helps perk them up.
Herbal tea does not re-infuse well as it does not really contain any "tea" leaves from the tea plant.
If you are making tea in a teapot, preheating your teapot by rinsing it out with hot (even boiling) water before brewing reduces the loss of heat during steeping. If too much heat is transferred from the steeping water to the teapot, the water may not be hot enough to brew the tea correctly. Also, preheating your teapot will help you keep the tea hot for a longer period of time.