1. Upgrade at Defensive End.
Kyle Vanden Bosch is hands down Detroit's worst player, let alone starter. In fact, he was rated the worst 4-3 DE in the league by ProFootballFocus.com. It's clear whatever intangibles he brings to the table are no longer a major factor and the Lions need to move on. Bjoern Werner and Damontre Moore are candidates for Detroit's first round pick, while Cincinatti's Michael Johnson is a potential free agent candidate. If nothing else, they just need to go with Lawrence Jackson as their starter (who they should most definitely re-sign).
2. Re-sign Gosder Cherilus.
Cherilus's early years as a mediocre (at best) talent have really put a sour taste in Lions' fans mouths, but in 2012 things were different. Believe it or not, Cherilus graded out as the league's second-best right tackle with the fifth-highest pass block grade out of all NFL tackles. The Lions need to lock Gosder up longterm.
3. Upgrade the Outside Linebackers.
Analysts and fans alike point to the secondary as the Lions' biggest weakness, but offenses could run at will this past season and that had a lot to do with the linebacker play. DeAndre Levy, who occasionally made big plays, has proven to be a backup level talent. If the Lions re-sign him I sincerely hope that they do not use him as a starter, though he is young enough that he might be able to improve on his game still (not to mention he had to play behind the league's worst defensive end). Justin Durant plays well against the run, but was often exposed in pass coverage allowing for tight ends and running backs to turn short passes into long gains. Tulloch had a down year, but was also playing through a knee injury, so I expect him to bounce back next season. I doubt the Lions will spend their first round pick on a linebacker, but if they trade back far enough it would be fun to see Manti Te'o in Honolulu Blue.
4. Re-Sign Joique Bell.
He's no Jahvid Best, but he is far more dynamic than Mikel LeShoure. He consistently broke tackles and was an asset in the passing game. I fully expect the Lions to draft another running back, but Bell has proven himself to be a difference-maker on offense.
5. Sign Jarius Byrd.
Pleeeeeaaaaaaase. He is one of the best safeties in the league and he's only 26. He would instantly improve the defense and allow the Lions to move on from Louis Delmas (or pair the two up). Mayhew needs to make a big move this offseason and this should be it.
6. Extend Stafford's Contract.
While Stafford may never be an elite NFL quarterback, he is clearly giving this team a chance to win every Sunday and at only 24 years old the Lions should make sure he sticks around for a while. Stafford's cap numbers for the next couple years are also fairly prohibitive and a contract extension would allow for Mayhew to surround him with more talent and upgrade the defense.
7. Re-Sign Chris Houston.
Houston is not an elite talent and should not be paid as such, but he was the most consistent player in the Lions defensive backfield in 2012. I don't believe it would be a huge blow to the team if they had to let him walk, but he is a talented back and an asset to the roster.