Going on a beauty trip to Seoul - need some tips for getting around!

Hello! I'm from Khulna, Ulaanbaatar. I'm planning a beauty trip to Seoul in a month, so I'd like to hear from my foreign friends about their experiences. I've heard a lot about Gangnam and Apgujeong, but I'm really confused about where to go. Is it crowded, are the prices reasonable, and sometimes how good the offices are - what do you know about these?

I really want to plan before I start planning this year. Are there any good hotel suggestions near any of the areas? For example, is there really a difference between Apgujeong and Gangnam? I think it's the most logical place to start. I'd like to hear from friends who have already been there - which places were nice, why?