In order to get a better idea of what the structure of the level is going to be and what is going to happen in it, I find it important to put the ideas down on paper. Then, I use this support as a base, which will be improved as I discuss the level with other people.

An example of Level Design Draft (clic to enlarge)

The work in progress map based on the Level Design Drafts, showing the initial blockout and early scripts.
Note that the speed of the mine cart is adapted to the player's speed, so that the cart is never too far away nor too close to the player.