So I'm writing a novel myself and the main character is called Jasper. Whenever he falls asleep, he goes into the dream world type thing. Same dream, same characters, same scenes. When he falls asleep, he wakes up in the real world. But... but when Jasper's in the real world I write him in third person and when he's in the dream I write him in first person. When he's dreaming, it starts randomly in through a chapter but at the end of the chapter he normally wakes up from the dream. Any tips writing this?
Your idea is quite creative. You better stick to third person narrative so that your narration goes smooth and you can even differentiate between dream and real life easily.. Writing in third person also gives you the liberty to explain thoughts of more than one person to the readers while writing in first person restricts you to only Protagonist's PoV. Make sure you create a good and interesting conflict.
There's a narrative style called an epistolary novel that can have multiple 1st-person narrators. The story is presented as a bundle of letters copied verbatim – copying letters word-for-word was like sharing a social media post in 18th Century. No one got confused because (generally) it was explained at the start that the next part is copied from another letter.
Les Liaisons dangereuses and Frankenstein are both epistolary. In Frankenstein it's a letter within a letter (within a letter). Les Liaisons dangereuses works like correspondence in chronological order, with some additional letters from minor characters to fill plot holes.
Your dreamstate POV can be introduced as a dream diary, essentially an epistolary story within the story. The protagonist records everything he can remember from his dreams, starting at a random point already underway and narrating up to when he woke up. His memories of the dream quickly fade to vague impressions soon after he is awake (and sometimes he goes back to sleep), so he started keeping the diary just to confirm the dreams are repeating, and later to piece the longer dream-story together. He's trained himself to write his impressions of the dream as soon as he wakes from it, and doesn't always remember writing in the diary the next day.
Once you have established that the diary is written in 1st-person and "real life" is in 3rd-person (by having the protagonist read from his diary), you can then jump between the two narrative voices without any transition.