Aim to exercise every day (just walking a couple of miles is brilliant exercise). If you don't manage it every day, don't worry - 4 times a week is pretty good.
Never skip meals, eat protein, carbs and fruit/veg at every meal. Try to avoid pre-prepared food (cook it yourself so you know whats in it!)
Cut right down on alcohol, caffeine, extra fat and sugar.
Don't go hungry but have sensible portions (as you get older your body needs less calories than it used to, to maintain the same weight - yes, unfair, I know!)
Know your weaknesses - eg. if you love biscuits, don't have them in the house. I lost half a stone in 3 weeks just by cutting out alcohol, and I didn't drink more than 15 units per week before.
Be honest with yourself about what you're really eating.
Tell everyone you know that you're 'being good' so they can encourage you!