Not to pander, but in general, if you have treated the car well, especially the interior, the fabric should show little dirt. However, the seats tend to repel stains. If you have a dirty spot I'd start with a rag that was just damp with water and see how that works out for you. And then I'd go from there up to a light detergent. Don't apply liquid to the fabric directly.

I make it a point to vacuum the interior regularly, especialy the seats, to prevent dirt from being ground in through normal use.

It has been said:
Hybrid drivers come in 3 flavors, greenie, techie and cheapie. Pick any 2.
2005 Prius, Melinium Silver over gray, package 5 (AI)