Poor Koukouvagia - it's not easy is it?
A handy pocket book calorie counter does help - eventually you'll know off by heart what weight of food has how many calories per ounce etc. Or with fruits and veg, how many cals an apple or banana or potato etc has on average.
The main thing is to watch out for is how much fat is used in the cooking. Our old friends butter, cream, cheese, oil, salad dressings etc. And to trim most of the fat from any meats. Your grill (broiler), steamer, poacher and microwave will become your best friends.
If you are cooking your veg without (or with a minumum) of oil, you can just make a rough guess of the cals. The only fruit to beware of is avocado. Yep, they are healthy, but lots of cals.
Meats - don't eat a serve of meat larger than the palm of your hand (especially if you have REALLY huge hands :) )
Alcohol can be a killer cal wise, so can all the usual nibbles that go with drinks.
Cooking spray oil is a blessing as its really hard to get lots of oil into a meal. Fresh salads will become one of your new best friends - make a big bowl of it at the start of the day, and if you feel incllined to snack, grab a bowl of it, couple of lo-cal crispbreads, a good book and snack to your heart's content. And veg soups, and stir frys - so much variety there. Use spices, garlic, ginger and so on to your foods to make them more interesting.
Keep it going - write down a list of what you eat for the day with a calorie amount (including any tea/coffee/drinks) and aim for your total allowance. Some days will be under, some will be over, then average it out over a week. Weigh yourself only once a week - day by day can be depressing :)
Eating out is much harder to guess how many cals, just try and choose what sounds the best choice cal wise.