To become that icon of style, that rolemodel of vampires and corpses alike, follow these ten simple rules and you'll live the rest of your undead life as a certified goth!
Step 1: Dye your hair. Black. Other colours, like red, white or green, take many years of experience and must never be combined with anything other than black clothes (see step 2). Highlights are acceptable if the colours are not too flashy.
Step 2: Change your wardrobe. Black is your new middle name. Colour must be avoided at all costs, with the exception of dark red. White is only acceptable if it makes up less than 5% of your total look. Anything that would be fitting for a Romanticistic noble(wo)man, if black, is acceptable. Combine this with anything from modern S&M, like chains on your trousers or handcuffs connected to a collar.
Step 3: Change your record collection. Throw out the Beach Boys, the Spice Girls, the Beasty Boys, and everything else that has "boys" or "girls" in it. Anything that is remotely cheerful has got to go. Instead, buy Cradle of Filth, Evanescence, Marilyn Manson and Bad Religion. Anything that has a weird name, looks weird, sounds like someone clearing their throat and which your parents will never ever accept in the living room.
Step 4: Throw your morals out the window, too. Being a goth means you're a slut (male/female). Consider it your only chance at getting laid looking like that.
Step 5: Paint your nails. Yes, this goes for guys too - in fact, you're lucky, since this is probably the only subculture to accept it besides the local transvestites. Black is again the colour to choose.
Step 6: Paint your face. As surprising as it may be, it'll not be black, but white. Imagine you've been indoors without seeing the sun for a very very long time - which is probably true.
Step 7: Additional makeup includes eyelashes (black), dyed eyebrows (black), and lipstick (black - or, if you're a real pro, red). This is not mandatory for guys, but encouraged. Dark eyes are compulsary, though. Coloured contact lenses are optional for both male and female.
Step 8: Get pierced. You know, those pieces of metal through skin - they go into every part of you that one can imagine. And I know you can imagine quite many places. Yes, including that and those. At the very least, have a ring in your nose or eyebrow - preferably both, connected by a silvery chain. But know that there is no such thing as "too many piercings". And yes, people will find out (see step 4).
Step 9: Act like you're high on cannabis - which is probably true. This means you criticize and complain about everything (particularly physical exercise), sit around all day doing nothing, and talk at great length about next to nothing.
And finally, step 10: You talk, think, sing, act and write about only one thing: death. It is the sole topic of conversation. Celebrate it, adore it, worship it, fear it, overcome it - your life evolves around death. And the best thing is that you even look like it.
You are now a certified goth!
But don't cheer - goths don't cheer.
P.S. I did write a serious piece on goths, located here.