The water you use is very important to the quality of your coffee. Use filtered or bottled water if your tap water is not good or has a strong odor or taste, such as chlorine.
If you’re using tap water, let it run a few seconds before filling your coffee pot, and be sure to use cold water. Avoid distilled or softened water.
A general guideline is called the "Golden Ratio" - one to two tablespoons of ground coffee for every six ounces of water. This can be adjusted to suit individual taste preferences.
Check the cup lines or indicators on your specific brewer to see how they actually measure. And remember that some water is lost to evaporation in certain brewing methods.
Your brewer should maintain a water temperature between 195 to 205 degrees Fahrenheit for optimal extraction. Colder water will result in flat, under-extracted coffee, while water that is too hot will also cause a loss of quality in the taste of the coffee. (However, cold brew does not need any heat.)
If you are brewing the coffee manually, let the water come to a full boil, but do not over boil. Turn off the heat source and allow the water to rest a minute before pouring it over the grounds.
Always allow your coffee - or any hot beverage - to reach a comfortable temperature before enjoying (specifically below 140 degrees Fahrenheit).