In the View menu, turn on Show Grid (g) and Snap to Grid (b). Showing the grid will allow you to see a grid over your map which can provide a good guide to follow. Snap to grid will make your paths follow the lines of the grid exactly, for extra precision.

Minimize your use of nodes - a path will run straight from one node to the next. The fewer nodes in your path, the more likely it is to run straight!