I was up beyond the 400 lb mark when I first got on my bike.
What I learned has already been stated.
Cadence, I used to do harder gears, because I felt like I was getting more power for my rotation. I have eased up on the gears, and my feet don't hurt as much. The amount of pressure I was putting on my peddles was unreal to me.
My hands and forearms were killing me until I talked to my LBS. I wanted gloves or new grips. When I told the guy how new I was, he says. I will be glad to sell you a pair of gloves, but I think its more likely your grip on the bike. Apparently, I was gripping on for dear life and had my elbows locks. So I was apparently He explained I just need to loosen up.
I loosened my grip., I unlocked my elbows, When I hit a bump or a dip or something, I let it go through me instead of bracing for it and trying to stop it. This has alleviated all of my pain.
The pain in my Arse got worse when I bought a bigger saddle, or even a gel cover. I just ride what my bike came equipped with.