1) Heat water to the correct temperature
In the picture below, you'll see the correct temperature for different kinds of tea. Notice that the stronger the tea, the higher the temperature. 

2) Measure the correct tea to water ratio
So...believe it or not...you can't just throw some tea in some hot water and expect it to turn out perfect. The correct amount of tea in the correct amount of water is SO important.

3) Steep for the correct amount of time 
Surprisingly, leaving the leaves in for over a minute or under a minute can make the biggest difference! Though people have different preferences, you should stay around the suggested times below. I like my tea strong so I tend to over-steep rather than under-steep.