Formal:
* Bien, gracias. ¿Y usted? (Good, thank you. And you?) - This is the most polite and formal way to respond.
* Estoy bien, gracias. ¿Y tú? (I'm well, thank you. And you?) - This is slightly more informal but still respectful.
Informal:
* Bien, ¿y tú? (Good, and you?) - This is a common and informal way to respond.
* Más o menos. (So-so.) - This is appropriate if you're not feeling great.
* Genial, ¿y tú? (Great, and you?) - This is a more enthusiastic response.
More Specific:
* Soy una persona muy sociable. (I'm a very sociable person.) - This is a good response if you want to highlight your personality.
* Me gusta pasar tiempo con mis amigos y familia. (I like to spend time with my friends and family.) - This is a more personal response.
Humorous:
* Estoy sobreviviendo. (I'm surviving.) - This is a funny way to respond if you're feeling overwhelmed.
* Estoy como un tomate, rojo de la vergüenza. (I'm like a tomato, red with embarrassment.) - This is a humorous way to respond if you're feeling shy.
Remember:
* Use the appropriate level of formality depending on the situation.
* Be genuine and honest in your response.
* If you are asked "Cómo eres?" it's a good opportunity to share a little bit about yourself.
You can also add other details to your response, like what you're doing or how you're feeling. For example:
* Estoy bien, gracias. Estoy estudiando para mi examen. (I'm good, thank you. I'm studying for my exam.)
* Estoy un poco cansado, pero estoy feliz. (I'm a little tired, but I'm happy.)
The most important thing is to be natural and friendly in your response.