Turbo Mode highly recommended. (Hold shift and click the green flag to turn Turbo Mode on/off.) You can add tiles to the level at your mouse-pointer by pressing the z, x, and c keys. Pressing z adds/removes a solid tile, pressing x adds/removes a reward tile, and pressing c adds/removes a punishment tile. (Reward tiles are basically the path the AI should take, and punishment tiles are basically where the AI shouldn't go.) Level changes will only appear after the current iteration is done. You can change where the AI starts at by clicking the screen. Set "Mutations?" to 0 to turn off mutations. (Uses the current best equations without making any changes to them.) Press the q key to hide/show the "Mutations?" variable.
It's not good at learning how to traverse areas that look similar to areas it has already learned how to traverse but that require different movement patterns to get through. Mostly, this means it's hard for it to turn around.