What the dry leaf tells you before you brew anything
COLOUR. Bright or dull green means a green tea and a cooler, shorter brew. Dark brown-black twisted leaf means black tea and near-boiling water. Mixed green-brown with reddened edges means oolong. Pale silvery-downy means white tea. Very dark compressed material means a dark or aged tea, and boiling water. SHAPE. Needles and flat pressed leaves suggest Chinese greens. Deep green needle-like fragments with dust suggest Japanese sencha, especially if some of it is powdery. Tightly rolled balls are oolong and will need room and time to open. Long wiry twists are black tea. A compressed cake or brick needs breaking before anything else. SIZE. Whole leaf brews slowly and forgivingly. Small broken particles brew fast and punish a long steep — a bag-grade tea in a pot needs seconds, not minutes. SMELL. Roasted and toasty means a roast you should brew hot. Fresh, marine or grassy means a green tea you should brew cool. Smoky means what it says. Almost no smell at all means either a very light white tea or a stale one, and the brew will tell you which.
A cautious first attempt
Deliberately under-brew. It costs nothing to add time and it is impossible to remove it. Use a moderate ratio — around 3 g to 200 ml if you have scales, or a rounded teaspoon of leaf to a mug if you do not. Use water around 80°C for anything green or pale, and just off the boil for anything dark or roasted. Steep for one minute. Taste. Then adjust once. Thin and pleasant means give it more time. Bitter or drying means less time and cooler water next attempt. Interesting but faint means more leaf, not more time. If you have enough leaf, brew two mugs side by side at different times rather than sequentially. The comparison teaches you far more than two separate attempts an hour apart.
Read the wet leaf afterwards
This is the step almost nobody takes and it is the most informative one. Tip the used leaves out and spread them. WHOLE SHOOTS with bud and leaf attached: hand-picked fine material, worth brewing carefully and worth re-steeping. UNIFORM FRAGMENTS with cut edges: machine-harvested or deliberately broken, brew short. REDDENED EDGES with green centres: partially oxidised, so it is an oolong and will take several infusions. UNIFORMLY BROWN AND SUPPLE: fully oxidised black tea. STILL PARTLY UNOPENED: your steep was too short or your vessel too cramped, and there is more in the leaf. BRITTLE AND DARK WITH NO SUPPLENESS: over-roasted, very old, or both.
When the packet is in a script you do not read
Look for the numerals, which are usually Western even where the text is not. A weight in grams, a temperature in degrees, a time in minutes and a year are all recognisable, and a sequence like 3g / 80°C / 60s is brewing instructions in any language. Japanese packets frequently give harvest and packing dates in a yyyy.mm.dd form. Chinese packets often carry a net weight and a production date. A four-digit number on a pu-erh wrapper may be a recipe code rather than a year. If there is a photograph on the packet, it usually shows the brewed liquor colour, which tells you the category immediately.
The two things worth not doing
Do not throw boiling water at an unknown green or white tea. It is the single most common way to ruin a tea you were curious about, and the damage is not recoverable within that cup. Do not commit the whole packet to one method. Brew a small amount, learn what it is, then decide. An unfamiliar tea is a thing to investigate over three or four sessions, and treating the first cup as a verdict on the tea is how good tea gets written off.