Knock the mud off first. Let dried dirt firm up, then brush it away before it works into the weave. A soft brush and a little warm soapy water handles most everyday marks on canvas without any need to soak the whole shoe.
Machine wash only when they really need it. Pull the laces and insoles out, drop them in a mesh bag with a towel to cushion the drum, and run a cool, gentle cycle. Frequent washing breaks down the glued sole bond, so treat it as an occasional reset rather than routine.
Air dry, never tumble. Heat warps foam midsoles and unglues vulcanised rubber. Stuff the shoes with paper to hold their shape and draw out moisture, and dry them somewhere airy out of direct sun so pale canvas doesn't yellow.
Protect and rotate. A fabric protector spray helps pale canvas shrug off stains, and giving trainers a day off between wears lets the foam decompress and the linings dry, which does more for how long they last than any amount of cleaning.