Prop your mirror against a wall or on the back of a door. Make sure you put it somewhere with ample space to move around and dance.
Find lessons online. Whether you want to learn ballet, ballroom dancing or hip hop, the key is knowing where to look. YouTube is an ideal place to find various dance styles. If you've exhausted the slew of YouTube videos available, plug your dance of choice into a search engine to find lessons.
Look for lessons by reputable dance professionals online. "Dancing with the Stars" dancer Karina Smirnoff, for example, is an instructor for the website learning2dance.com. Dances such as swing, tap and the hustle can be found here, with varying levels of difficulty. Many are free. Dance champion Forrest Vance also provides lessons in cha cha, salsa, the waltz, among others, on his personal website.
Go for comfort. Loose-fitting T-shirts, shorts and socks are the way to go. Once you've identified your dance style, get started.