Drastically reduce things such as bread, white pasta, noodles, sugar, cakes (although these last two are a bit obvious
) and potato in the form of crisps, chips, roasted or mash.
If you want to keep eating potatoes, pasta and bread, opt for wholemeal/granary types but keep it to a minimum and baked potatoes are best.
Be wary of fruit juice - it might be tasty and full of vitamins (depending on the juice) but is loaded with sugary calories.
Also, if you get a craving for chocolate, try a couple of squares of dark chocolate (letting them melt slowly in your mouth). It's richer so should satisfy you for less. I've also heard of people freezing chocolate as it takes them much longer to eat it which results in them eating less of it.
Alternatively try munching on some dates. Medjool dates are the nicest I've tried so far - they have the texture of the caramel from millionaire shortbread and are lovely and sweet with lots of fibre and vitamins. As with fruit juice though, don't overdo it with these.