All I had to do was to completely eliminate sweets, crisps and fizzy drinks from my diet. I lost 10 kg in first 3 months, but I noticed that I was loosing less and less each month. So, to sustain weight loss, I've started to cycle to work (unless the weather's crap) and jog 3 times a week (5km per session). In total no more than 4 hours per week of extra physical activity. One year later and I'm healthy 75 kg (from almost 100), with BMI score of 24 (previously 32) and it's going to stay that way. This isn't a diet, it's a lifestyle change. I still have occasional cheat day, mostly during a night out or when I go the cinema, but no often than twice per month. And honestly, this isn't as hard as I thought. The hardest part was to commit and move my lazy ass. Once you do your first step, it's getting easier with each day, especially when you see results.
ps. and don't even bother with quick fix diets or anything super drastic. In a long term this stuff never works. Trust me, I tried. What's worse, because how drastic those method are, they leave bad taste in your month and discourage you from any future commitments. .