Shorten his routes
Towards the end of the season, Stefon Diggs was running deeper routes which didn't help the offense for two reasons. The first was that the offensive line was struggling at this point of the season protecting Josh Allen so longer developing routes weren't ideal with Josh Allen having less time and usually resulting in errant throws. The second is that these deeper routes are not the strength of Diggs' game.
In the final five games, Diggs' average depth of target was 12 yards or more in four of those games. In the first 11 games of the season, there were only three games where he had an average depth of target over 12 yards.
Stefon Diggs is one of the best route runners in the league and does a great job creating separation on those short routes. According to Pro Football Focus, Diggs was the third highest graded wide receiver on slant routes and the best wide receiver on out routes.
Lauren Gray wrote that Diggs didn't run the out route much compared to the two other wide receivers. He only had 16 targets over the course of the season but caught 15 of those passes and this is something Ken Dorsey should look to incorporate more this season.