Heaven is the opening world — plan it as your reading lesson
The description lists Heaven first, and it is where the game's two permanent rules teach themselves: every step adds +1 speed, and one wrong move returns you to the start.
Run Heaven in three passes: a reading pass at controllable speed, a full-speed repeat, then a push one section past your previous best. That loop costs less total time than sprinting attempts, because Heaven's resets — like every world's — send you back to the start of the run.