I've come up with a new procedure for making lines -- rivers and roads, but also other lines -- twist and turn a bit. It depends on the clock face directions described in the previous post. It produces lines that are less extreme than those made with the technique in the blobs and lines post, but which are still interesting.
For each line or line segment you want to make twisty, assume that it is divided into quarters. The first quarter of the line stays the same; the direction of the other quarters may be different. Roll 2d12 and read from left to right, with the first die representing the second quarter of the line (ending at the midpoint of the line) and the second die representing the third quarter of the line (starting at the midpoint.) These indicate changes in direction. For example, a 12 result means the line veers due north. The length of the detour is four hexes by default, but you can roll 2d4 and read from left to right for the length of the segments. Connect the endpoint of the third quarter of the line to the original endpoint to make the final quarter of the new line.
Rivers: Each change in direction is caused by higher ground that forces the water to find a new course downhill. Lines are 1 hex wide except where they join larger bodies of water.
Roads: Each change in direction is caused by either difficult terrain or some other danger in that terrain. Roll a d8 and use the result indicated on the terrain table. There may also be a hamlet or outpost at that location. Roads are narrow and pass through hexes, rather than filling an entire hex.
Secondary Terrain: Lines of secondary terrains that extend into grand hexes don't have to be straight. Halve the result of a d4 roll for length, though. You can also apply this technique twice to one line to create a line of varying thickness.
Hex Edges: To avoid perfectly straight transitions between two adjacent terrain types, treat each hex edge as a line and roll 2d12 and 2d4 to provide variation. Skip hex edges that have lines of secondary terrain extending from them.
Coastlines: No reason you can't apply this to curved lines as well as straight lines. Take one side of a lake or sea and apply the hex edge technique to keep it from being bland.