Horizontal writing (가로쓰기) and spacing (띄어쓰기). It was not a thing.
Also, breaking syllable blocks up just like when you write Latin alphabets (풀어쓰기) was suggested -- not adopted though. Like writing "ㅎㅏㄱㄱㅛ" instead of "학교."
Another suggestion, in 1954, was simplified Hangul orthography where you write 갓 instead of 같, 갇, 갓 as they make the ...
Hangul orthography, Ministry of Culture, Sports and Tourism, public notice #2017-12 (effective from March 28, 2017.). Here.
A booklet PDF that explains (in Korean) the both
There’s a good official booklet that explains them all and answers quite a lot of questions on Korean language Stack Exchange. For orthography and pronunciation(not at ...