*Wear dark clothing: This is not essential, but it is a deciding factor in how other gothlings will view you. Stick to dark colours; black, burgundy, reds, purples...A lot of goths, including myself, limit their wardrobe to strictly black (stereotypical, I know, but we look cute as hell!). Wearing bright colours are premises to be judged as a poser. Try not to wear anything too cheery, and remember not to be a weekender!
*Make the Goth transition a gradual one: There is a lot to learn about the gothic subculture. One cannot become "goth" overnight. Do not change your style, make-up or hair-colour/style too drastically. Do it when you feel you are ready to. Going overboard with the look will cause some gothlings to turn up their noses at you.
*Read Gothic Literature: Anything by H.P. Lovecraft, Poppy Z. Brite, Edgar Allan Poe, or any classic horror novel are great ways to broaden your reading material and learn about gothic literature, and possible the history of the subculture itself.
*Maintain your style: Dress original, learn from trial and error, and be comfortable. Wear clothes YOU like, not what others tell you THEY like. Make sure that you dress goth at least a majority of the time. It is great to change styles, but make sure you are comfortable with the change.
*Be Yourself: Do not pose off of a friend, the movies, or the mainstream. Be who you are; an individual. Being unique is what being a gothling is all about!