I'm very much in agreement with cjohnson, but that happens a lot. For me to make the changes I needed to live healthier, I had to make those changes one or two at a time. There wasn't really a day where I woke up and said "today is the first day of my new healthy lifestyle forever - Amen", although I've had those days in the past, it never worked long term for me. Basically what I did was to write everything down, study myself and then look for ways to improve my life one habit at a time.
The first thing I did to get started was to write down what I ate, when I ate, where I ate and what I was thinking while I ate it. I didn't actually diet I just tracked my eating habits. I know that sounds extreme, but it really helped me pinpoint problem calorie areas. As it turns out I was eating breakfast like 3-4 times every morning. None of it bad, but like 1,500 calories BEFORE lunch. So definitely an area for improvement.
Another area for improvement was my amount of workout time. Before I got serious about my healthy lifestyle, I got myself to the gym 1-2 times a week for an hour, and took a 1 hour line dancing class every week, so 1-3 days of workout and 4-6 days off. Now I workout almost every day for an hour and even on my "off" days I take a long walk up to the grocery store to pick up the paper, so I've reversed it 5-6 days of workout and 1-2 days off. It also occurred to me that I was DRIVING 1.55 miles in each direction to the gym so that I could walk 5K on the treadmill. How stupid is that? So now I run/walk up to the gym and lift weights for an hour and run/walk home.
So I say making changes one at a time is a good approach, but if you want to jump in with both feet and go hog wild and that works for you, I say go for it.
Starting weight: 244.6 lbs. 10/01/09
Pounds lost: 80.6 lbs
Current weight: 164 lbs
Goal weight: 120 lbs
Weight to go: 44 lbs
Goal Date: 1/1/13