There's usually two types of Tower Defence pathing as far as I've observed over my years (and many games of Tower Defence / Tower Wars!):
1) Large lanes to build in; mobs will take the shortest route from spawn to end point. You often end up making mazes with your buildings in these.
2) Single lanes to build around; mobs must walk the path laid out and these will often include loops where you've got opportunity to build in the centre of. You often end up building close to turns and loops to maximise opportunity for your tower to hit any given mob more than once.
Then some TDs will allow users to "block" the path -- usually in these instances a blocked path will result in mobs actively attacking the structures in the way.
There's also a variant of 1), in which you have a big open space and several waypoints that mobs will visit. The optimal strategy for these TDs is to create a maze, but one that will require the mobs to travel several times through the center of the arena where you place the strong/short distance towers. Gem TD is an example of such TD
1) Large lanes to build in; mobs will take the shortest route from spawn to end point. You often end up making mazes with your buildings in these.
2) Single lanes to build around; mobs must walk the path laid out and these will often include loops where you've got opportunity to build in the centre of. You often end up building close to turns and loops to maximise opportunity for your tower to hit any given mob more than once.
Then some TDs will allow users to "block" the path -- usually in these instances a blocked path will result in mobs actively attacking the structures in the way.