While every tea is different, there's still a few basic guidelines that apply when you're brewing any tea.
For regular daily brewing of your teas in a teapot or mug, roughly 1-2 minutes (with 1 Pinch per-person) will be perfect for most teas. Less than one minute will probably result in a weaker brew, and longer than 2-3 minutes will give a bitter brew (see below about avoiding bitterness).
If you're brewing your tea the traditional Chinese way, then you'll normally want to use more tea, and brew it for less time. Typically, most teas brewed in a gai wan porcelain cup need only 30 seconds to release a good, strong flavour.
If you brew your tea for too long, the brew will often become bitter and tannic - this is a quality the Chinese call se which means 'dry and bitter'. In fact you don't need to brew your tea for that long. Especially with finer quality teas, sometimes 30-60 seconds is all you need to bring out the flavour, and 4-5 minutes will almost always result in bitterness.
If you're looking for a stronger taste in your brew, don't brew the tea for longer! The trick of the trade is to add more tea leaves, but keep the brewing time the same - this will normally help bring out a stronger taste.
You can infuse your teas multiple times, but as you rebrew, lengthen the time a little bit. Normally the 2nd brew won't be much longer than the first, but the 4th brew might need to be approximately double the time.
You should experiment with your favourite teas to find the perfect taste for you, but if in doubt, just check out our detailed brewing guides for each of our teas.