Tracks in the Sand: Advice on Railroads and Sandboxes in Tabletop Gaming

From the introduction: New GMs have many questions regarding railroading: How do you deal with railroading? Do you just create a scenario and improvise the consequences of your player's actions throughout the whole thing? Or do you somehow give them a limited array of options for which the outcome you already know? Or do you do something else? Where does "trying to keep them on the quest" stops and railroading begins? Is it the same as forcing a quest if the consequences of not taking said quest are too dire? This PDF is a collection of tips and advice for how to correctly use railroads and sandboxes.