Ok, this may be an understatement, but you may hear me bang on a bit about seasonality. Rather than get up on my soapbox, I'll just keep it brief. Some retailers react to trends, some to the seasons. Try and seek out the latter, you'll recognise them as they won't stock asparagus and the like all year round. More than likely these are the people who will speak most animatedly about what they have 'new in' and 'what's eating best'. 
But how do I know what's in season? There are many websites and charts around that will tell you, Eat the Seasons is one I use the most, but after a while, you will learn by intuition from what tastes good at what time of year. Nothing makes a winter supper like roast root veg and the taste of summer is the juice that dribbles down your chin from eating a fresh strawberry.

So eat fresh, eat now