You want your diagram to be simple to read and not overwhelm your viewer with too much information. One of the most important things to look out for is appropriate padding and consistent spacing between the elements in your diagram.
Unfortunately, there’s no general rule of thumb for these principles. It’s often a good idea to just play around with the placement of each item until it looks good. You want to give your station text some breathing room from the lines and symbols but not too much space that they feel disconnected. Try to have at least ½ inch of breathing room around the entire document, but not more than 2 inches.
You will also want to distribute elements as often as possible so that stations and station names are evenly spaced out where they occupy similar spaces. You should be somewhat familiar with the Align and Distribute tools (shown above). You'll want to align common elements to the same axis, and distribute items on lines periodically depending on where they are in the design. There is a video below that shows you how to use each tool. There's also a game you can play, The Elements Game, to help you apply your knowledge.