A tip when grouting: Wipe excess grout off as soon as possible otherwise it can leave a film on the tiles which doesn't come off. After much scrubbing and googling, I found that wiping the tiles off with lemon juice cleaned them beautifully.
Another tip I saw on a show: When grouting (which is a toothpaste consistency, use your spatula to spread the grout and then scrape off excess grout. Sprinkle with some dry grout. This will absorb a lot of moisture. Leave on for 5 minutes then rub off and buff with crumpled up newspaper.