Your tea is only as good as the ingredients used to prepare it.  Good quality water and proper brewing time are essential for a flavourful cup of tea.
Loose, fresh tea and fresh, aerated water along with proper steep time  = mmm goodness.
- Use fresh cold water. In areas with poor tap water, use bottled or filtered water. Never use water from the hot water tap. Let the tap water run for a few seconds until it is quite cold this ensures that the water is aerated (full of oxygen) to release the full flavour of the tea leaves.
- Use one level teaspoon of loose leaf for every  6 ounce cup you are making
- Bring water to a rolling boil. Don't let it boil too long, as it will boil away the flavour releasing oxygen and result in a flat tasting cup of tea. Pour boiling water on tea leaves or tea bag.
Brew 3 to 5 minutes
More on selecting the right water temperature
Black, Dark Oolong, Herbal - These types are best prepared with water that has come to boiling. Don't let the water boil too long or the oxygen content will be reduced and the tea will taste flat.
Green, White, Green Oolong - These types should not be prepared with boiling water as this will cook the leaves and destroy their flavour. Japanese greens tend to taste best with water at 170-180º F. China green teas tend to taste best with water at 185º F. Generally, the finer the green tea, the lower the water temperature should be. To brew green tea without a thermometer: pour the water at the moment that bubbles begin to rise from the bottom of your kettle, or bring the water to a boil first and then let it cool for two to three minutes before pouring.
More on steeping for the proper length of time
The time it takes for tea to brew depends on the leaf size. The smaller the leaf, the faster the tea infuses. Until familiar with a particular tea, steep for a minute or two, then taste. Pay attention to the taste rather than the colour. When the tea tastes right, serve or pour off all the liquid to avoid oversteeping. Here are some general guidelines:
Japanese Green Teas: 1-2 minutes
Chinese Green Teas: 2-3 minutes
White Teas: 2-5 minutes
Green Oolong Teas: 2-3 minutes
Dark Oolong Teas: 3-5 minutes
Black Teas: 3-5 minutes
Herbal Infusions: 5-10 minutes
Some green, oolong and white teas are good for multiple infusions. Just add fresh hot water to the pot and increase the steeping time slightly for each subsequent infusion. Repeat until the flavour starts to fade.