It was realising that I'd passed the point over overweight and gone into 'obese' (and, I have to say, DIY completion that meant I could stand on some scales at home) that triggered action to lose weight. Accepting that it is a long project is the first task... and that is difficult because you know it means real change rather than a temporary push.
I faffed about for quite a while until I looked at where I needed to get to and broke it down and decided to set a goal of losing 5kgs every quarter. This has really helped. Note that lots of people would be expecting that as a reasonable and sustainable monthly goal, but like financial budgeting where the tendency is not to factor in the annual expenses into a monthly budget, this slower pace accepts that eating is not a precise thing and that whatever reductions/restrictions you set yourself, they won't be achieved every single day... and don't need to be. I find that nearing each 'finish line' is motivating and isn't too far off to think I can put it off. As some others have mentioned, the MyFitnessPal thing which says "If every day was like today you'd weigh X in 5 weeks" is very helpful.
Note that I didn't actually achieve 5kgs a quarter but I have still got myself into a healthy BMI range and I feel this 'system' works well enough for me to have it as a goal for the first quarter of 2014 (to get to a point which feels right for my body and build)
I've also found it helpful to set a variety of other goals which are not explicitly about weight loss - eg increasing the number of lengths I can swim, C25K, meditations. It's always worth testing how well the goal is working for you - it is a tool not your master.