The marker particles may be included as is, shortened, or dropped altogether. All three cases are common.
- 나는 고등학교 학생이다 (I'm a high school student) - including 는 makes it more natural in this case.
- 난 고등하교 학생이다 - same, but 나는 is shortened to 난, which happens a lot in conversation.
- 나 여기 더 있고 싶지 않아 (I don't want to stay here anymore) - subject particle won't add any information - so dropped.
- 날 그만 놔 둬. (Leave me alone) - objective case contraction: 나를 -> 날.
There is an array of contractions to shorten or smooth the combination of common pronouns like 나 and 너 with the maker particles.
* 나(1st person, plain) - 난(나는, subjective 는), 내가(나가, subjective 가), 내(나의, possessive), 날(나를, objective).
* 저(1st person, lowered to be respectful) - 전(저는), 제(저의), 절(저를).
* 너(2nd person, plain) - 넌(너는), 네가(너가), 네(너의), 널(너를).
* location marking particles which can be contracted - 내게(나에게 - to/at me), 네게(너에게 - to/at you), 내게서, 네게서, etc.
There are other more obscure ones too but they are not as important.