The best advice I can give is START SLOW. You didn't get out of shape overnight and you aren't going to get into shape overnight. Injuries that may occur make it VERY difficult to get back into it. If you haven't done much in a while start with some walks and then brisk walks.
I walk with my best girlfriend about 20 miles a week (5 miles a day, 4 days a week). So this won't be new to me. When I quit smoking, I put on about 25 pounds, from eating when I was bored. I'm the kind of person who needs to eat just about once a day, or eat just a tiny bit throughout the day (snacking, basically). My really good friend Sunni is trying to sell me on the "no S" diet (No snacks, no sweets, and no seconds, except sometimes on days that start with "s"), but I don't think it's right for me, because I have to snack throughout the day, otherwise I shake so bad, I can't hold a pencil. Literally. I've had employers (in the past) who made me take drug tests, because they thought I was coming down off of something (the problem was that I wasn't allowed to eat at work).

At the time, I was devastated that I wasn't being trusted, but now I understand better just how odd a reaction it is. *shrugs* It's just my body, nothin' I can do about it.
DO NOT use a scale. Scales lie and do not allow for fat loss vs muscle gain. They can make you lose motivation with incorrect feedback. Get a tape measure and measure your self (arms, chest, belly, legs, etc) before starting your program. After you begin measure yourself once per week.
Okay! I'll do that as soon as I get home from my vacation (We're sight seeing and property checking and visiting family about 2000 miles away from home at the second). That'll be Wednesday morning of next week. I'm really pumped about doing this. Is it gonna make my muscles big? I want big muscles after I lose all of this crappy fat.

What you will not be able to calculate is the weight you will not gain from continuing to eat poorly.
That's true, but what I can do is calculate how much I've gained recently, and the path that I would have continued to go on with a line graph, as well as what happens when I start this program. That WILL show the difference, as well as where I might have ended up if I'd continued down the path I was heading (see that? I WAS heading down it. But not anymore!

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