Hello! Foreshadowing takes on different shapes depending on the author/writer and their writing style. When it comes to foreshadowing danger, consider the following:
- Pacing: In most cases, when danger approaches or is imminent (regardless of whether the character(s) know it or not), sentences are often short and choppy. Longer sentences could have hidden clues that may be revisited later. For example, what is the environment like? Are there changes in the environment and/or characters?
- Patterns and symbols: Is there an object or symbol that appears multiple times? Or does a character have a weird habit? Repetition can be a useful hint giver, especially if its presence or mentioning is more frequent as the story progresses - or has to do with blood, death or other high risk factors, like a missing character or object of importance.
- Sound: Imagine that you are in the story with the characters. In many genres, sound and the lack of it are popular clues that something isn't right. Is the silence too long and tense? Or is the happy party interrupted by something breaking, someone screaming, etc.?
- Textual warnings: Many works subtly mention the danger or risk factor before it substantially appears later on. For example, is there a habit or tradition the locals have that MUST be kept? Or do the characters have a specific instruction from an authoritative figure, who refuses to explain why they must obey? A common trope with danger is that it comes up when rules are broken...
Of course, these are a few guidelines based off of the horror/thriller genre. Hope this helps; happy sleuthing!
