Luke
I guess my #1 piece of advice for finding overvalued or undervalued teams would be this simple core strategy: don't believe the hype.
The Raiders were widely projected to be one of the worst teams in the NFL last year. They opened up the season by covering three straight (at the closing number) and seven out of ten, consistent moneymakers. The Jets were widely expected to be awful as well; but, like Oakland, they covered four out of five to open the season; solid short term moneymakers.
On the other end of the spectrum, look at Atlanta; a team that was expected to contend for the NFC South title, but a squad that ended up being a real bottom feeder. The Falcons opened up the season 2-8 ATS; a dramatically overvalued commodity. Down the stretch, the markets had them undervalued and Atlanta covered five of their last six, despite winning only twice in SU fashion.
Or look at Jacksonville. Through the first half of the NFL season, the Jags were on pace to be one of the worst teams in modern NFL history while going 0-8 SU, 1-7 ATS. What happened next, following their bye week? The Jags got slightly better; the markets never adjusted and Jacksonville backers cashed winning bets in four of their next five games.
The betting markets often zig when they should zag, and vice versa. Teams rarely hold their value (or lack thereof) for more than a month or so. I'm always looking to jump on or off these 'morphing' squads as the season progresses and the markets over or under-react to what they've seen; markets that are reactive, not proactive.
Hope this helps,