If you get a mark on suede, use a clean pencil eraser.

Rub VERY gently with a pumice stone.

Suede is a skin, not woven like a fabric - treat it like your own skin! You need to lift the dirt off. The best thing to do is brush suede clean with a soft to stiff brush. Use mild soap (like clear shampoo or ecover washing up liquid) with the brush, but try not to saturate the suede. Sometime dabbing with sticky tape helps to lift out the dirt, and a fine emery board or rubber should help with marks and restoring the nap.