Hi!! I've been wathing dramas for 4 years, but lately I've been wathing only Korean dramas. I'd like to watch some Japanese or Taiwanese dramas, but I don't know what to watch. I like stories about school, music, love. Can you help me?? ^^

These are all Taiwanese Dramas:
Fated to Love You
Drunken to Love you
Hana Kimi - If you can get past Ella Chen's acting
Just You
Office Girls
Woody Sambo
Sunny Happiness
ToGetHer
Fabulous Boys- A nearly shot for shot remake of You're Beautiful

I haven't seen MARS or Autumn's Concerto but they are from what I hear really good classics.
Japanese
Liar Game (not really school or music.A bit of romance but great)
Itazura na Kiss (Remake of It Started With A Kiss)
Q10 
Nodame Cantabile
Rich Man, Poor Woman
Gakkou no Kaidan

You may have seen Korean versions of some of the dramas though.

Taiwanese 
Just You (Seconded)
Fabulous Boys (preferred this to Korean version You're Beautiful) Seconded 

Hope this helps.Sorry there is not more from Taiwan as I tend to drop them.
Hey there, I'm not that sure about your request, so you want dramas about all three (school, music, love) or just those categories?
Well either way, I can tots help you with taiwanese since I've seen alot. For Jap not so much since I just started as well. Please bare with me.

Taiwanese:
So firstly since you want to start on taiwanese dramas I think you should watch the 'classics' back when Taiwanese dramas were the bomb, basically during their best time. 
- Autumn Concerto (2009) --> this is a true classic about love, fate, revenge and will honestly bring tears to your eyes.
- Prince turns into frog (2005) --> definitely a classic as well and it has all the clique settings but back then those weren't clique. 
- My Lucky star (2007) --> Love and revenge involving jewellery and significance.
So these are three of my personal favourites and they're honestly some of the best taiwanese dramas so you should definitely check them out first. 

For your categories, I'll just put down the ones that are good/famous.
School:
The only one I can remember now is the taiwanese version of 'Playful kiss', if you've seen the k-version. The taiwanese one is actually the oldest one.
- It started with a kiss (There is also season2 called: "They kissed again")
- Hana Kimi --> this is also a manga/anime remake, the k-version's called 'To the beautiful you'"

Music:
Taiwanese dramas don't have alot of music ones, though even if there is I might not know either since I don't remember favour this genre.
The only one I remember so far is called 'Fabulous Boy's which is the taiwanese remake of 'You're beautiful'

Love:
Since this topic is basically everything, I'll just give you some general good ones over the years. 
- Love keeps going (2011) Pretty good one, 13 eps I think
- Pleasantly surprised (2014) this is has cooking factors and I think is a pretty good one in recent years

So far just go with these. 

As for Jap dramas, I haven't seen much so I can't help you. :(

 
you should watch Moon River (taiwanese) it's currently airing and it's hilarious, it kinda resembles BOF/HYD in a way but the story and events are totally different.
another taiwanese one im currently watching is MARS and up till now it's really good, it's a lot deeper though.
I also watched a movie called ''secret'' and it has music, romance and it's at a school. Note; it's a fantasy, i didn't realise it and it took me by surprise. Really awesome movie.

as for japanese school dramas, hmm..im trying not to name the ones mentioned already and not the tragic ones;
switch girl, really funny, cute romance
pin to kona
kingyo club
asuko march (this one doesn't really have THAT much romance, rather friendship)

movies;
l-dk, say I love you, ao haru ride, strobe edge,kinkyori renai, kokoro no ito
Thank you for all the recommendations ^^ I've already watched some of them, but still thank you. I've never finished Autumn Concerto, but I think I'm going to restart it very soon >.<
School, music, & love: Shut Up: Flower Boy Band (kdrama)
Music & love: Mary Stayed Out All Night (kdrama), My Lovely Girl (kdrama), You're Beautiful (kdrama)
Music (and I honestly don't remember if there was love in there too): Beck (jmovie), Bandage (jmovie)