To fit in with emos, there are three important elements - attitude, looks, and music. The basis for the music and looks starts with the attitude or mindset so let's explore this first.
Attitude
Emos tend to be more quiet as they spend most of their time exploring their internal world. This in turn, makes many emos seem somewhat introverted. However, being introverted or not is not something you can choose to become. If you're not introverted, that's perfectly fine. What's really important is that you spend time alone looking inside of your mind and emotions. Of course, I don't advocate shutting yourself off from the world. And I don't think emo means not being able to have a good time and laugh with friends.
Emo is really about being aware of your inner emotions and expressing them in all sorts of ways. Emos are just people who understand that life can be tough.
Some people get heart broken, some get excluded because they like things that most people don't like, some are born in abusive families, some get misunderstood by others - whatever it may be, they're just people put in situations where we did not ask for. They realize these sufferings and they express them through all sorts of ways. Some emos cry, some cut themselves, some make art (with their blood sometimes), some express through music, some scream their lungs out, and some just share these feelings with other emos who understand (thus forming the emo community!). The point is, emos are not afraid to accept and express their emotions.
Emo is also about introspection, and in moderation, it may have benefits as it can help you grow in life and discover who you are. So to a degree you feel comfortable with, start exploring your own feelings and reflect on life issues from time to time.
Spend some time pondering even in public. In this way, you can relate to other emos as they talk about their inner world experiences.
Looks
Emos may dye their hair various colors, but the main color is black. The black hair was probably influenced by Goth. Black means a couple things like sulking, fear, mysteriousness, and confidence so make of it what you will. Although there are various styles, the hair is generally long and covers one side of the face. This covering of the face shows that one is not looking to outer world as much (introspective) or one does not want the world to look in (shyness). Emos also wear tight fitting clothes such as jeans and t-shirts. Tight clothes and skinniness represents sensitivity and fragility. The tightness helps make the skinniness more visible. Studded belts are also popular. Girls wear skirts, usually, black, red, or plaid with leggings or stockings. Emos also wear shoes that are worn out. Personally, I'd think it's a way for us to show that we're not afraid to be real. Or it could just be a cool stylistic thing.
As for accessories, they tend to wear glasses that are thick horn rimmed glasses that are black framed. This signifies that one is intellectual and reads a lot. A lot of emos read books that are very philosophical and hard to understand. In a way, emos are like nerds with an edge. Jewelry and piercings are generally for younger people like high schoolers or young college kids.
Music
As for music, listen to music that brings out emotions in you and that you can relate to personally. In addition, you will want to be able to discuss music with other emos so you can have emo friends. All of this builds your emo credibility. Emo music is a mixture of influences from Punk, Indie, and Goth.