This article is from the Hiking Boots FAQ, by Chris Gilbert email@example.com with numerous contributions by others.
Care of fabric boots is pretty much the same
as for leather. If they are not waterproofed you can use a water
repellant such as Grainger's G-Sport, which you simply spray on
when the boots are clean and dry. You need to apply a couple of
coats and allow a few hours for the boots to fully absorb it. The
coating should be re-applied as necessary, e.g., after you have
washed and dried the boots. To keep the boots clean, simply brush
off any excess mud, and then wash them in clean warm water. The
best way to dry them (as with leather boots) is to stuff them with
paper and leave them in a warm place. You can get away with
putting fabric boots next to a heat source to dry but beware any
leather or suede reinforcing patches. If the boots are a fabric/suede
mix, you can use a special brush to revitalise the nap of the suede
bits. You should do this before applying any water repellant.