It depends on the dance style you are doing. For standard dance and latino, a very important part of your body is the legs.
They give you speed of movement and you use them when you decide you want to move slower or faster, or when you want to create stillness moments (for example, when you want to move very fast and then suddenly stop).
Another important part of your body is the arms. In latino, for example, the arms are very important because when you are doing a fixed position, you can create multiple movements just by using your arms and hands. For instance, during flamenco (a latino dance), dancers hold in their hands something called "castanets", which make a sound (they are a percussion instrument). Therefore, it is very important to have good control of their hands when dancing.
Hope this helped and good luck ❤️!
I've been a professional dancers for the past 10 years. I went to college for dance and have trained since I was 3 years old. If you focus on just one body part, you're missing out on building strength as a whole. Every dancer is different and every style is unique and will inform what muscles might be more active, but the focus of a dancer is to be prepared and well rounded. So instead of narrowing your scope to focus on training a certain part of the body, add new movements and exercises and new dance styles each time you train. Try yoga. Try Pilates. Try CrossFit. Try kickboxing. Never stop being curious about other ways to move your body and never think you're "done" training or learning. There should never be an end to your knowledge-seeking in the dance world. So try it all. Train it all. Build the best possible dancer you can be by staying curious and treating the whole body as your instrument. Hope that helps.