Depends on what kind of hob it is. I have a black ceramic one which has had all manner of things burnt onto it over the years. I squeeze a cloth full of water over it, spray it with mr muscle kitchen cleaner, then leave it for about 20 mins. Then I gently scrub it with one of those wire scourers (not the soap filled ones), then wipe it down with kitchen paper and it comes up good as new every time.