It's all just maths. You count what goes in. You count what you exercise off. If there's a deficit you lose weight. If there's a surplus you gain it. And really it IS that simple.
Being organised is THE KEY! Plan your week in advance. Make a menu plan and a shopping list and hang it somewhere in the kitchen that you can access easily. Mine is on the inside of my pantry door;
This is not a diet, it's a way of life.
It's mostly in your head. If you tell yourself you can't do something, then you'll be right. But if you tell yourself you CAN do it, you'll be right AND successful!
Nothing tastes as good as skinny feels. I'd read this when I was fat and thought "whatever". But now I live this motto. And if you don't buy it, you can't eat it. So don't.
When you're having a crappier than crap day, go and exercise. Nothing seems as bad after a good sweat.
Chunkability; The breaking down of something overwhelming into something manageable. I published my mini-goals here on my blog - in the sidebar so they were always visible, and celebrated every 2.5kg with a little reward.
Comparison is soul destroying. there will always be someone that has a better week, bigger loss, higher burn, whatever. This is your own race. Run it at your own pace, and keep improving your own personal best.