At #1, quite simply, I hope the Lions do the smart thing and open up contract talks with Aaron Curry, Jason Smith, BJ Raji and Matt Stafford. The real point is that in making sure that their player is in the fold right away, the player has the best chance to succeed as a Lion. That said, with the #1 overall pick you need a player that can help you - and I'm not sure that Stafford is that player yet - but the first 3 appear to fill important needs.
Curry helps them at SLB, where they currently have an undersized marginal player in Ryan Nece. For one this would allow them to play alot of man under with his strength, opening up Ernie Sims on the other side and effectively boosting their size on defense.
Smith is a bit raw on technique because of his 2-point stance from college, but he has the build, strength and smarts to start out as a left-guard in year one and move to left tackle after learning about the speed and skills of the pro game. Of course if he really shows well, the Lions could do a whole lot worse then Jeff Backus competing with Manny Ramierez for the left guard spot.
Raji fills a huge hole in the middle of the Lions defense where their top 1 technique DT is Chuck Darby, an undersized part-time player who is better suited in rotation as a 3rd down player.