I started out by listening to koreanclass101 podcasts then started studying hangeul and its rules... then a little bit of grammar. Since then, I've been slowly building up my vocabulary, when I don't understand a word I just search it up through naver dictionary which also provides sample sentences.
I got used to watching variety shows without subs too cos at the time, my bias didn't have subbers so I got quite accustomed to relying on myself to understand a show even if just a little bit. I also try to translate netizen comments for past time and that is how I also extend my vocabulary and learn new slangs and figure out how they abbreviate terms and stuff.
At the moment, I'm making an attempt to read and understand a novel, I would search up the words I don't understand and write it down so I could go back to it and remember it even more. I would reread the passage and it kinda works.. :D