I lost 25 kilos in 7 months before I had my first baby, and kept it off for 8 months til I got pregnant.
The best thing I did was break it down in to min goals.

And here comes the uber geek part.

I made an excel spreadsheet that calculcated my current and goal BMI based on the weights I entered, and it also graphed my weighloss so I could see the progress I was making.

I put i the start date and allowed for 0.5 kilo loss per week.
Then I had a column for how much I actually lost, and it worked out my new weight, and how much I had to lose per week after that to still get to my goal on schedule.

Of course, we arent all computer nerds like me

I also went to a meeting once a week where you get weighed, like weight watchers but community run/ not for profit. so you pay like $4 a meeting or something

I exercised or went to the gym 4-5 times a week, cut down on softdrink, snacking between meals and began eating breakfast.

The person who said they got happy hit it on the head too - exercise puts you in a better mood, andt he more you do the better you feel.
If you want to do something like that but don't have the computer brains to pull it off - like me, try the calorie king site, there is an online tool like this, that charts weight loss and size changes.