Korean does not have articles as they are found in English and there is no distinction between definite and indefinite articles. Thus learners will often confuse the usage of a, an and the. This can lead to students saying things like:
* I bought new car this week.
* an asterisk denotes an ungrammatical sentence
Adjective order is is often an issue leading to errors such as:
* I bought a Samsung big television.
There is often confusion between countable and non-countable nouns.
In verb forms, Korean speakers often confuse the present with the future due to mt influence. There is also confusion with the past simple and present perfect simple. All this means that the use of verbs needs to be carefully explained and covered.
There are also often issues with subject-verb agreement.
* I told to him
The basic sentence structure of Korean is very different from the usual Subject Verb Object of English and so learners who tend to translate will often produce very garbled sounding utterances.
You should spend time explaining sentence structure and emphasizing the simplicity of SVO in English.