Simply follow the path at the start of the 'proper' game, following the red arrow painted on the wall and making your way through the linear path and simple puzzles.
Eventually you will reach a room with an outline of a man on the wall. In front of this is a round brass button embedded into the floor. Run across the button, and speedily make your way around to the bottom of the wall where a lift will activate. The agility orb (allowing you to jump much higher) is at the top.
Don't miss the hidden cassette tape room here too! Using your new-found agility, jump around to the shelf on the north-east wall and jump over the room boundary to find your first collectible. Good luck with the rest - just try jumping out of every room you can!