Have to start drafting well again, it really is that simple. What put the Pats over the top in 2014 and 2016 was that they were getting a ton of production from rookie contracts. At the time of SB49 they had drafted Solder, Vereen, Cannon, Chandler Jones, Hightower, Collins, Ryan, Harmon and Stork in the previous four years. That's a ton of talent of cheap contracts. By SB51 a lot of those guys had aged out of their rookie deals and either left or received a big raise, but they still had Butler, Thuney, Garoppolo, Flowers, White, Mason, Andrews, Butler, Ryan and Harmon all producing on rookie deals.
Now that the 2014 draft class has played out their rookie deals, there just isn't a real base of cheap talent to build on because the 2014-2017 drafts didn't produce a lot of hits. I'm a big fan of Mason, Flowers, Wise and even Jonathan Jones. I even think Thuney's a fairly solid pick, but that's just not enough guys. And unless the 2018 picks turn out well it's likely to get worse, since the 2015 draft class is about to become FAs, and the two best players we've drafted since 2014--Flowers and Mason--are both in the last years of their rookie deals.