Just Give Them the Snaps...
This one has kind of been beaten to death, but fans (including myself) were beating the drum all season long to find more snaps for Green. At this point in his career, he is a better tight end than future Hall of Famer Antonio Gates. He is taller, faster, and a better blocker.
In 2013, Ladarius averaged over 22 yards per catch (on only 17 receptions), and vastly improved his blocking. He saw only 370 snaps to Gates' 996, and that number has to come up in 2014.
There is currently a lot of uncertainty among the teams receivers (Alexander and Floyd's injuries, Royal's contract). If Green can improve a bit more as a route runner he could very well become Rivers' number two weapon behind Keenan Allen.
I loved Kendall Reyes going into 2013, but he definitely disappointed. Reyes is certainly more talented player than Lissemore, but the way he was used in John Pagano's defense, he won't reach his potential. Lissemore is a more "traditional" 3-4 defensive end, as he is able to clog up running lanes as a 2-gap player rather than shoot a single gap like Reyes.
Lissemore has played well in a limited role with both the Cowboys and Chargers, but only managed 217 snaps last year. Even with a tiny snap count, he was the second-highest rated player for the Chargers' defense (yuck) according to Pro Football Focus at +6.6. If Pagano is not going to adjust his scheme to the strength of the player (crazy thought, right?), he might as well adjust the players to fit the scheme.
This one is a long shot, but would give the team the biggest out-of-nowhere boost. Although he did miss his entire rookie season to injury, Williams will be entering his second training camp. Also, the nature of his injury (torn pectoral) shouldn't affect his blinding speed, which is something the defense lacked in 2013.
Cornerback was an absolute disaster in 2013. Shareece Wright led the team in snaps played at corner with 802 (out of 1017), and wasn't very good. Richard Marshall was second on the team with 637 and was also awful. We all know how bad Derek Cox is and about the injuries that plagued a secondary that was not talented to begin with. The Bolts will address the cornerback position in the offseason, but Williams should definitely get a good chunk of playing time.
Let Them Keep Getting Better...
Johnnie had some really bad games, but also some really good games. He was an excellent run blocker in nearly every game he played, but his mechanics as a pass-protector were sloppy and he failed with assignments such as picking up blitzes.
Offensive line coach Joe D'Alessandris is one of the best in the business, and if he can put Troutman on the right track after what was essentially a rookie season, he can crack the starting lineup and be an excellent guard. Especially since Jeromey Clary could be a salary cap casualty and Chad Rinehart is a free agent (as well as injury-prone).
Ingram surprised a lot of people when he returned to action about 7 months after a torn ACL. Not only did he surprise with the quickness of his return, but he also surprised with how well he played. Melvin did not get a second training camp to work with the defense, but he returned and got stronger every week. He set the edge as a strong run defender, and also managed 13 QB pressures (sacks + hits + hurries) in his final 4 games.
Melvin should be at full strength going into next season, so look for his pass rush ability to improve. He could stand to be used more creatively (Thanks again, Pagano), but even if he's not, Ingram could very well be in for a breakout season in his second full campaign.
Addae played extremely well this season for an undrafted defensive back. Over the first 13 games, Addae played 234 snaps, about 18 per game. He had a -2.7 rating over that stretch (PFF). In the final 5 games (including postseason) he managed 282 snaps, about 56 per game. He had an impressive +6.2 grade over that stretch.
The undrafted rookie was essentially the team's nickel defensive back, as he came in to play safety against 3-WR sets. That could change depending on what the team does in the offseason, but there is no denying the improvement of Addae. Regardless of who the Chargers do bring in, Addae has to see the field more in 2014.