To make a perfect cup of tea you should be aware of more than one thing. The thing is that different teas have different brewing requirements. Some teas can be steeped for long periods of time (particularly Tung Ting),but with other teas over-steeping can result in a beverage that is both astringent and bitter. Follow this basic directions and you will have a good cup of tea.
If using loose tea, the hot water need to circulate, so make sure that the leaves have enough room to fully bloom during the steeping process. The perfect container for this should be a large teapot with a strainer.
Tea bags do not really give the tea room to move around much during steeping, so if using tea bags, you should move the bag around a few times, during steeping, to help circulate the water.
You should measure your tea, 1 teaspoon per cup (8 oz.) of water is sufficient for brewing tea. Some teas, like white tea and tisanes, require more water for steeping, up to 16oz. Often tea containers will tell you exactly how much to use.
Proper water temperature can make the difference between a perfect cup of tea and something that merely resembles tea. Heavier teas, like black tea and oolongs brew best at boiling temperature, 212F. Lighter teas, like white tea, green tea, and some oolongs are better brewed at a lower temperature, such as 180F ( way to reach 180F is to let the water boil, remove from the heat, and let sit for a few minutes).
Heat the teapot before adding your tea leaves by adding some boiling water to your teapot and swirl it around. Pour it out and than brew your tea. This is done because we want to maintain the proper steeping temperature. Otherwise, the cool teapot would cool down the boiling water.
Don't over-steep because over-steeping tea can produce a cup that you won't want to drink. A general rule is the heavier the tea, the less time it should steep. Black teas will generally steep no longer than 3-4 minutes. Oolongs will brew closer to 4 minutes, and white tea can steep for 5-7 minutes.
For green tea different rules apply. The higher quality the tea, the longer it should steep. Cheap green teas, like bancha and sencha will steep for only 30 seconds. Genmaicha will steep for 2 minutes, and Tung Ting(technically an oolong, brews more like a a green) can practically steep forever and is often enjoyed gungfu style.