I want to say the action suddenly started and carried on.
序 · The move
1Put the verb of the action first (笑, 哭, 唱, 下雨).Is this the moment the action starts, not a direction it travels?
2Attach 起來 right after it to mark the kickoff.Could I swap in 下去 to mean keep on? If continue fits and start does not, 起來 is wrong.
3Leave 起來 at the tail; an object sits before the verb or rides 把 (把歌唱起來).Does the reading come out start to, with no upward path? If it reads as up off the ground, that is V起來1.
例 · Examples
1他一聽到hear (and catch)消息news就開心地happily笑起來break into laughing (onset)。
The moment he heard the news he broke into a happy laugh.
Same two characters, split job. V起來1 is real upward motion you can watch (站起來 = rise to your feet). V起來2 is the onset of an action that need not move at all (笑起來 = burst into laughing). Ask whether anything physically lifts; if not, it is sense 2.
了2 reports that a new state now holds (下雨了 = it is raining now). V起來2 catches the action at the instant it kicks off and keeps going (下起雨來 = the rain sets in). One states the new state, the other films its start.
✗ 他起來笑。 → ✓ 他笑起來。 (起來 follows the verb, never leads it.)
✗ 天黑起來下雨。 → ✓ 天一黑就下起雨來。 (the object 雨 slips between 下 and 起來: 下起雨來.)
✗ 她哭起來了一個小時。 → ✓ 她哭了一個小時。 (起來 marks the start only; a duration cannot hang on the onset.)
English burst out laughing or start crying front-loads the start word, so learners reach for 開始 and skip 起來, or read every 起來 as up and miss the start-to-do sense entirely.