As all others have said plan. I'd also add don't get hungry.
Don't skip a meal or have a small snack and then find yourself hungry later in the day surrounded by temptation.
Eat to satisfy your appetite.
Its not a diet its a long term sustainable way of eating if you absorb the ground rules. The ground rules include enjoying your food and really thinking and planning to have food that satisfies and interests you. Don't feel guilty for eating.
I lost about five stone last year - into this year. I now fluctuate a little more (up) than i ought around my target.
If crisps and chocolate are your thing then plan them into your week. If you're more of a drinker then check out the syns and plan in your drinks (one small word of caution on drinking is I find after a couple of glasses my control goes to pot and I stop counting syns. I find its best for me to generally stick to one large glass of wine, not from a syns point of view but from a control one). If you like everything well you get the chance to rotate your syns or go for smaller versions to have a selection.
One, off plan meal, getting the syns wrong, over indulgence is just that. Don't beat yourself up. Everyone over indulges sometimes. Whats important is to not let one meal out become a weekend off plan, a weekend off plan to be a week as an oh well may as well right this one off till next weigh in. Thats how a week of fluctuation thats probably a maintain/ on balance even a loss becomes a several pound gain.
Small regular losses add up. Don't ever fret its only half a pound all the losses add up and you really can do it.