Baring psychological issues, it's really not hard at all to pick a diet and adhere to it. It literally requires a few hours of upfront effort and a bit of time each day. I was able to go from about 300 lbs as a 6'3" male to 210 lbs with significant muscle mass added by following a basic diet and lifting 3 times a week, and I literally started on a whim.
If you want to lose weight, I would start by getting an idea of what you already eat using http://www.myfitnesspal.com/
Once you get an understanding of your habits, head on over to http://iifym.com/iifym-calculator/ and select a diet plan which will make you the happiest (low carb, low fat, zone, stricty calorie deficit etc). Every morning, plan your meals using myfitnesspal and the output from iifym.
It's really that simple.