It's quite simple really...
Set up a spreadsheet in Excel or something similar, where you can enter your daily food intake, both in terms of energy consumed, and how much protein, carbs, fat and water you eat/drink.
One row per day in the sheet, and add daily weight (measured at the same time each day), and maybe a few key body measurements as well (waist, hips, thighs?) to each row. That way you can keep track of both how much you eat and how that affects your weight and measurements.
Get a good estimate of your daily energy need, and use that as a starting point - try to consume around 500 kcal less than that every day. Exercise should be factored in, so 500 kcal worth of cycling is as good as eating 500 kcal less (or even better, in fact...), so you could just as well add that too.
I did just that, and found initially that I consumed much more than I thought (and you have to be honest with yourself and really count every single thing you eat during the day!) and consumed far less water than is recommended. I should add that my water consumption calculation includes the "hidden" water in the food as well, not just the water I drink.
At the start, I only got around 1.2-1.5 litres per day in me, and that's far from the 2.5-3 l I've seen recommended. It took me three weeks to get up to that level. And when I did, as a bonus, my migraines became much less frequent.
All in all, I've managed to go from 79 kg (174 lbs) to 65 kg (143 lbs), and from a 97 cm (38 in) to a 79 cm (31 in) waist since May 1st, when I started this project. (I'm 1.78 m/5'10".)
I've also used several methods to estimate body fat, and kept track of that as well, and found that I've only lost around 1-1.5 kg of muscle in the process - or around 10% of the total weight loss.
It's really about how much you eat, and not really what you eat. Eating good and healthy food just makes it easier to eat less - it doesn't allow you to eat more in terms of energy, if fat loss is the goal.
Good luck!