Advice from Bewley's, Ireland's premier tea emporium:
How to Brew a Perfect Cup of Tea:
Fill a kettle to the required level with freshly drawn water.
This may sound quite obvious but there is a tendancy to re-use boiled water or top up a partly filled kettle. This de-oxygenated water does have an adverse effect on brewing.
Heat an earthenware or china tea pot (stainless steel pots tend to taint the brew) by filling it first with hot water and pouring it out.
Use one teaspoonful of tea per person plus 1 for the pot. When using teabags, use one teabag per person. Add boiling water.