I (like everyone else) will assume you mean social dancing, like swing.

In which case, my number one advice for efficiently learning is DON'T BE SHY about asking for dances.

So many new people in the swing community have very slow growth because they don't pro-actively seek out dance partners. The ones who get best the fastest are the ones who spend the majority of songs actually dancing, NOT just hanging around hoping someone will ask them to dance!

Most mid-sized cities have at least one swing community. Most decent-sized colleges have a swing club, and they almost always allow non-students to participate. Just Google "<city> swing". I recommend social swing to ballroom.

Classes are good, and will teach you things step by step, but you then have to go to open dances to practice what the class taught. I would say at least 3 hours of open dance per hour of class. (These are cheaper too!)

What kind of dance? My experience of things that are helpful in learning social dance (swing, contra, etc.) 1) Try the other role sometimes - if you normally dance lead, try dancing follow so you discover the good and bad things leads sometimes do. 2) Ask for feedback from good dancers. 3) Ask leads how they do particular things you want to learn. Follows normally can't teach you much about leading because they don't know how to do it.

Find a social community around dancing. The main reason that I learned swing dancing and stuck with it is that there was a large and friendly circle of swing dancers in the Bay Area, and multiple dance venues (some of them free!) every week.

I see in a reply of yours that you're interested in salsa dancing. By far the most important factor in getting better is to quickly achieve a level of competency that makes salsa socials really fun. I don't think I've gone more than 7 days in the last 2.5 years without attending a salsa social, and this has been the biggest factor in my improvement.

You may already be at this stage since you said you enjoy dancing, but if not I suggest you learn the basics from a friend or a class (I would spend no more than 10 hours on this stage), and then force yourself to attend a bunch of salsa socials, until you start really enjoying the experience.

Once you've reached this stage, you've solved the motivation problem, and now you can optimize towards becoming a really good dancer (if you even want to at this point - it's not necessary to reap the majority of the benefits).