WordVale
Every learner's mistakes are predictable from the language they already speak. Korean and English differ in a handful of structural ways, and almost every persistent error a Korean speaker makes traces back to one of them. Knowing which one is what turns a habit into something you can fix.
Articles: the hardest thing in English, and it isn't close
Korean has no articles. English requires one in front of most singular countable nouns, and the choice between a and the encodes something Korean marks differently — whether the listener already knows which thing you mean.
The rule that helps most is not the textbook one about specificity. It's this: use the when you could point at it and your listener would nod. "I went to the bank" — they know which bank, yours. "I need a bank" — any will do. When you introduce something new, it's a; the second time you mention it, it becomes the.
Plurals hide the problem. "I like dogs" is correct with no article; "I like dog" means something else entirely, and unfortunately means food. Zero article with a plural is the safest default when you're unsure.
/l/ and /r/, and why hearing comes before speaking
Korean has a single liquid consonant, ㄹ, which behaves like [l] in some positions and a tap [ɾ] in others. English treats /l/ and /r/ as entirely separate phonemes, and swapping them changes the word: light and right, collect and correct, play and pray.
Production follows perception. Train the ear first, with minimal pairs, before drilling the mouth. Then the physical difference: for /l/ the tongue tip touches the ridge behind your top teeth and air flows around the sides. For English /r/ the tongue tip touches nothing at all — it curls back or bunches in the middle of the mouth. If your tongue is touching something, you are producing /l/.
Final consonants and the extra vowel
Korean neutralises consonants at the end of a syllable and doesn't allow most final clusters. English is full of them. The result is an added vowel: desk becomes "desku", milk becomes "milku", strike becomes three syllables.
Two things help. First, English final consonants are often barely released — the /k/ in desk is closer to a stop of airflow than a full sound, so you can under-pronounce it rather than over-pronounce it. Second, practise the cluster attached to the next word: "desk is" glides into "des-kiz", which is how it actually sounds in speech.
Word order, and the missing subject
Korean is subject-object-verb and drops the subject freely when it's obvious. English is subject-verb-object and almost never lets you drop the subject. "Yesterday movie watched" is transparent Korean structure; English needs "I watched a movie yesterday."
The one that persists longest is the dummy subject. English requires a placeholder where Korean requires nothing: It is raining. There are three people here. Neither it nor there refers to anything — they exist because the grammar demands a subject.
Prepositions, which no rule will save you from
Korean uses particles that attach to nouns; English uses prepositions that attach to verbs, and the pairings are arbitrary. You depend on, listen to, arrive at a place but arrive in a country. No logic connects them.
These cannot be reasoned out, only met repeatedly. Which is the argument for learning them inside sentences you encountered rather than from a table — the sentence carries the preposition along with the verb, and they stick together.
What to do about it
Read, and save the phrases where your instinct would have chosen differently. Not just unknown words — the ones where you'd have said "arrive to" and the text says "arrive at". Those are where your English actually improves. The routine for making them stick is here, and the phrasal verbs collection covers the other half of this problem.