Having said this I can't totally dismiss calories, although I never count them myself. It's true if you eat way too many or way too few it will be detrimental for your health. Most peoples intake will be regulated by their appetite, others will over-eat til they're uncomfortably full and some people will limit themselves by calorie counting (something I discourage as it tends to lead to poor food choices). Whatever the situation there's only so many calories you can eat in a day so you should use this amount wisely.
What I mean by this is maximising the amount of nutrients you take in for the food you eat. Of course you can take supplements, but the nutrients in food are usually more bio-available (useable) by the body. Obviously this means eating plenty of fruit and veg and lean proteins but also actively avoiding the big calorie wasters:
Sweets and chocolates - very calorie intensive and low in nutrient value - for a sweet treat swap for fresh or fruits or a small amount of dark chocolate (rich in antioxidants).
White processed carbohydrates (white bread, pasta, breakfast cereals, biscuits and crackers) - most of the vitamins have been removed in processing which is why the manufacturers often advertise that they've added them back. For carbohydrates with a higher nutrient content go for brown rice, wholemeal and granary pasta and bread, rye bread, oat cakes and new or sweet potatoes.
Non-fresh fruit juices and soft drinks - generally most drinks contain wasted calories so the first choice is to swap these for water but otherwise go for fresh (as in drunk within two hours of juicing) juices and smoothies. Don't be tempted to drink low calorie soft drinks either as the artificial sweeteners in them are not good for the body.
Ready meals, canned processed foods and junk foods - pretty much devoid of useful nutrients. Healthy dinners can be made in minutes and alot of supermarkets offer healthier fresh steam cuisine options, whilst the city is full of healthy food outlets such as Leon, Pret and Chop'd making junk food unnecessary.
If this all sounds like no fun at all remember that it can be good for you (psychologically) to have a treat every now and then. I usually recommend eating healthily 80% of the time and unhealthy foods 20% of the time. When having a treat find the tastiest version of whatever you fancy and enjoy every mouthful - don't waste your treat calories on poor quality junk, make them count!