One thing Democrats could do—with basically no strategic downside—is to hammer home the message that voters should ask for and return their mail ballots as early as possible, which makes it more likely they'll be included in tallies on election night.
In most states, mail ballots received by Election Day will be counted with other ballots on election day; in some states they'll even be counted first, in fact. It's ballots postmarked by E-Day but not yet received (allowed in some states but not all) that can cause a late shift.
But if Democrats return their ballots sooner, the late shift could be mitigated or even reversed. There's maybe the slightest hint of that already in North Carolina, where Democrats represent 49% of absentee ballot *requests* but 54% of ballots *returned* so far.