The reason I mentioned "British English" in my earlier response is because we differentiate between the noun 'practice' and the verb 'practise'. The clue clearly demands a verb, since it relates to the verb 'do'. The Sunday Express is a British newspaper - though there may of course be an American version - so if this refers to the former and you plan to enter the completed crossword for a prize, I'd strongly advise you to use the 's' version and not the 'c', Natalie!