become familiar with all this shit and youll be well on your way
proto-metal
blue cheer, sir lord baltimore, cream, deep purple, discharge, led zep, the doors
trad/prog/power/speed/whatever
motorhead, angel witch, diamond head, saxon, witchfinder general, mercyful fate, cirith ungol, manilla road, helloween, manowar, crimson glory, fates warning, jag panzer, running wild, queensryche, pagan altar
doom
pentagram, saint vitus, trouble, candlemass, cathedral, winter, dream death, skepticism, thergothon
thrash
venom, metallica, slayer, megadeth, anthrax, exodus, dark angel, sepultura, kreator, destruction, sodom, celtic frost, overkill
death
possessed, death, autopsy, sepultura (earlier), master/deathstrike, morbid angel, carcass, atheist, bolt thrower, at the gates, darkthrone (debut), entombed, dismember, carnage, suffocation, immolation, deicide
black
bathory, tormentor, hellhammer, sarcofago, mayhem, burzum, immortal, darkthrone, beherit, rotting christ, gorgoroth, graveland, enslaved, emperor, master's hammer, root, samael, thorns
you don't need to like all that stuff (obviously) but if you want a historical sense of metal these are all classic bands worth knowing. keep in mind a lot of them cross over into other genres, i just put them in the categories i usually associate them with