Varied Distances:
Varying the distances that players must jump from platform to platform. Longer gaps require more precise timing, as there is less margin for error.
Environmental hazards:
Environmental hazards like moving platforms, spike traps, increase the challenge by giving a penalty for mistimed jumps and restrict the player maneuverability.
Enemies:
Enemies are effectively moving hazards. They increase the pressure on the player, making otherwise safe areas unsafe and require that the player have a good timing.
Time limits:
Place a limit on the time the player has to complete the level. This increase their sense of urgency and requires greater precision.