The 24-year-old told the team's website: "Best shape of my life. I feel a lot stronger, quicker and faster.
"I've been paying attention in meetings. I wanted to make sure when I came back that I wasn't a step behind. If anything, I was prepared. I'd done conditioning, I'd worked out, I'd done everything possible to get myself ready for practice and the games.
"I feel stronger just all around, mentally, physically, just all around. When you don't have to worry about everything, it's just football, it's a whole lot easier just studying and everything. I just feel good. It's like I've said before, I'm in a great place physically and mentally."
Miller made 68 tackles, 18.5 sacks and an interception in 2012.