Well I started with Playful Kiss, so I definitely recommend it to watch it next :D Since you’re a beginner highschool/teenagers dramas are the best ones to watch :D
Here’s a list with dramas of this genre:  Reply 1997, Heartstrings, You are beautiful, Heirs, Monstar, School 2013, Devil Beside you, Why why love [the last 2 ones are taiwanesse dramas but they are pretty good too]
You can also try some jdramas too :D : Hana Yori Dango season 1 & 2 [jap. version of boys over flowers though to me this one it’s much better than the korean one] Buzzer Beat, Piece, Sprout.
When you get tired of this genre you can start watching more mature themed dramas like Secret Garden, Nice guy, That winter the wind blows, A gentleman’s dignity, My princess, The princess’ man, Goong, Coffee Prince.

Hope I helped you! ^^