Find the destination
Look at the balloon above a common train and match its colour to a town. Confirm the destination before changing a switch.
Trace a complete route
Follow the proposed track from start to finish. A short route is only useful if every connection leads where you intend.
Check signals and switches
Treat each junction as a decision point. Review its position before a train reaches it rather than reacting at the last moment.
Keep the layout readable
When adding track, preserve clear connections. If the network becomes hard to follow, review it one route at a time.