There is nothing that will make a bad tea taste good. It is also true that the best tea in the world, without the proper equipment, water, and technique, will turn out mediocre. Here are the critical factors to preparing the perfect cup of tea:
1. Water. Does your water have a taste? It shouldn't. Tea offers relatively subtle flavors, and the quality of your water will always trump the quality of your tea. In addition, hard water will draw out the flavor and astringency (sometimes called "bitterness") more quickly, whereas water that is too soft will yield a weak cup. Perfect water is filtered and retains 40-50ppm of minerals (usually calcium carbonate). Perfection may be hard to achieve at home, but a tea shop that doesn't bother to be perfect shouldn't bother to open.
2. Weight. Using the right amount of tea seems like an obvious requirement, but it is often overlooked. A "teaspoon per cup" appears to be the standard approach, but what is a cup? A "cup" technically is 6 ounces. But for many drinkers, it's a 12-ounce mug. As importantly, a teaspoon of Chinese Gunpowder could be two or three times as much tea (because it is tightly rolled) as a teaspoon of White tea (large, open leaves). A level teaspoon is possible with Rooibos, but utterly impossible with many Oolongs.
3. Temperature. Brewing all teas at the same temperature is like serving well-done steaks to all customers in a prime steakhouse or serving all wines chilled. It just makes no sense and defeats the purpose of buying quality leaves. The perfect cup is derived from a balance of time and temperature. Water that is much cooler than boiling will not properly release all of the flavor and essential elements of a black tea. Water that is too hot will release too much of the astringency and undesirable characteristics of a green tea.
4. Time. Twinings did a study years ago and found that the average tea bag drinker steeped their bag for 45 seconds. Given the Twinings recommendation of 3-5 minutes for a black tea, that's a massive problem for quality. As stated above, the perfect cup is derived from a balance between time and temperature. Whatever you do, don’t leave the leaves in the pot.
5. Equipment. Last but certainly not least, use the right equipment. A fine mesh filter will keep the particulate from your cup. Just make sure that you either brew loose in a pot or use a large enough filter that the leaves can expand. Consider dedicated cups and pots. It is not uncommon for tea shops to serve a soft green tea with a hint of Earl Grey, Jasmine, or even coffee that carried through from the beverage previously in my pot or cup. If you're serious about quality tea or running a tea shop yourself, you should be using a gram scale, a thermometer, and a timer.
Please consider providing detailed instructions on every package, including recommendations for weight (in grams and teaspoons per 6-ounce cup of water), temperature, and time. Many customers won't bother with all the steps, but some will. By offering this information, you make it possible for your customers to get it right, and you communicate the simple truth that to get the perfect cup of tea requires a little attention to detail.