Perfect 3-4 Sentences
The general writing advice is "don't throw your character directly into the action at the beginning because we don't care about the character yet." However, depending on your genre, the writing advice could say "don't throw a character directly into the action unless you can make people care in the first 3-4 sentences."
So, how can you perfect the first 3-4 sentences when it comes to "throwing the character into the action?"
1st sentence: hook the reader with an immediate statement or confession.
2nd and 3rd sentence: capture the voice of the narrator and give a sense of the mood.
4th sentence: Drive in the interest with the narrator stating facts while trying to gain back some control of the situation they find themselves in.
Do all this and it will leave the reader thinking: What will happen next?!