(Mind you, I was a goth years ago, so much of this is out of date. OTOH, the out of date stuff is what forms the goth stereotype, so there you are.)
Rule number one: Black, white and red are the only colors worth wearing. Okay, I guess now dark pink or emerald green might be okay. Whippersnappers.
Rule number two: Pale is good. Tan is bad.
Rule number three: Other people’s religious symbols are good, but only if they are large enough to blind a bull at ten paces. (Crosses, pentacles, ankhs, stars o’ David.) If anyone asks you what it means, sigh heavily and mutter that they wouldn’t understand.
Rule number four: Silver, silver, silver. No gold, ever.
That dress isn’t bad, actually. It will goth up well with either an obnoxious religious necklack or a simple velvet ribbon tied around your neck.
If you don’t have fishnets, drag out that pair of black pantyhose in the back of your drawer - you know, the one with a run in the thigh that you save for the long skirt? Make a few more rips and runs in them. Secure the edges with nail polish (clear) or hairspray (aerosol).
You can get black nail polish for 99 cents at the drug store - look for the Kiss brand. Also pick up some black eyeliner and deep purple or red lipstick.
Night of - don’t use foundation, or use foundation several shades lighter than you normally use. Make sure you blend it down onto your neck so you don’t have a mask line. If you don’t use foundation, put a generous layer of moisturizer on, and dust your face with baby powder. Use the eyeliner generously on both the top and bottom lids, as well as around your lip line, like you would a lip liner. Then apply the red lipstick and blend the black line into it. You can, if you’re good with makeup, also use the lipstick as a creme eye shadow, like this.