As others have said, take it one step at a time.
I wouldn't even focus on losing specific amounts by certain dates - just change on thing, then another - and see how you get on!
Don't set yourself up for failure by seeing it as a 'diet' or restriction - it's a change in your lifestyle, is all, and a change for the good.
I lost 40lb, two years ago and I have severe PCOS which makes weight loss 3 times harder for me than a woman without - it took me over a year to lose the weight and even at the end, when I could lose no more, I was still technically a few lb 'overweight' for my height - although down from size 22 to 12, so go figure!
Best tip I got is find out your MBR (metabolic basal rate). That's the no' of calories someone your weight & height needs, per day, simply to stay alive. Then eat to that. Eg: When I started, my MBR was around 1800 I think (I forget!) - I was surprised how much that was. For every 10lb you lose, review your new MBR. If you eat below that you'll be starving and more likely to binge and it may reset your metabolic rate too low. There are good tools for measuring MBR on
www.weightlossforgood.co.uk
My other best tip is use a site like Fitday.com. It's free and you can monitor your calories. Have a 'normal' day tomorrow and feed in to Fitday everything you eat - see - realistically - how much you're truly eating/drinking. Although Fitday is a US site, you can 'custom' feed in the foods you eat most often, and then it figures out not only your calorific intake but also things like % protein, etc.
In the end I lost weight using a ton of things - Paul McKenna's CD *I Can Make You Thin* (he did!), old Rosemary Conley books and mags from charity shops, fitness DVDs - and I took up jogging and yoga. Later on, I used Rick Gallop's Low GI books, and then Rosemary Conley went all low GI on us anyway, which helped! Used Fitday, this forum and a PCOS forum for support.
What kept me going when it got tough was thinking I'd rather be here for my kids 30 years from now, than not. And at first, it was a HUGE thing as the clothes at first fitted me better... then got too big. As your dress sizes go down, that's a massive incentive.
They say it takes 3 weeks to re-programme your brain to a big change, foodwise. I found the first week was the hard part. And indeed, after week 3 - it got easier and easier. Then the fitness was its own reward and motivating!
Good luck! Will be rooting for you.