Future revival plan for the Democrats
I really do think it was for the better for the democrats that Hillary Clinton did not win the 2016 election. If Hillary did win, she would definitely be a one term President. If Hillary hasn't died or suffered a serious health crisis by 2020, she would surely lose to any half decent Republican candidate. Also, the Democrats are facing a tough Senate race in 2018, with 25 Democratic senators vs 8 Republican senators running for election. Hillary is no where near as popular as Obama, so a 2018 election with President Hillary would be even a greater disaster for the Democrats than 2014. Plus the Republicans in Congress would provide an obstructionist roadblock against President Hillary's agenda.
With Democratic Congressional gains minimal in 2016 when big wins were needed to recover from the big 2014 losses, 2016 was a loss for the Democrats. We can only change the future, not the past, so this is what the Democrats needed for a revival plan.
Get their core voters to vote in every election, not just the Presidential elections
Young voters under age 30, minorities, and women make up the core Democratic voters that led Obama to victory twice. While Hillary won the majority from these core voters, it was well short of Obama's accomplishments, which is why Hillary lost.
During non-Presidential elections, voter turnout of the young and minorities drop significantly, which is why the Democrats lost so many Congressional seats and state governor/legislator seats. As we saw with Obama, the President isn't all so powerful. Congress must write legislation and approve it before it reaches the President. State and local governments are even more important because it is so much more effective to get legislation passed at the state and local levels, as opposed to being nearly impossible to even reach Congress. Having more members in Congress and state governors provides a larger and better pool of candidates running for the Presidency. Look at the start of the 2016 primaries, there were 17 Republican candidates vs 5 Democratic candidates, and the pool of Democratic candidates was so bad we only had 2 viable candidates (Hillary Clinton and Bernie Sanders) running.
While Obama was President, the GOP were using their majorities in Congress and state seats to their advantage for years to come. When the GOP won the House majority in 2010, they used their power to gerrymander the Congressional districts, which are drawn every decade from the U.S. Census. At the state level, the GOP were using their power in state governors/legislators to their advantage. The Republicans would often place voting restrictions, such as Voter ID laws and limiting or eliminating early voting for the purpose of suppressing minority voters.
Reach out to the white voters
This does not mean to follow the defunct Sailer Strategy of reaching out to only white voters and ignoring the minority voters. All voters are important and every vote counts. While the Democrats will not win the majority of the white vote, they need to reach out them. At 70% of the voters during Presidential elections and considerably higher in non-Presidential, special, and runoff elections (often surpassing 80%), white voters are still the large majority. When the Republicans surpass 55% of the white vote, it delivers a devastating blow to the Democrats. Democrats need to focus on all voters, white and minority.
Eliminate the superdelegate voting system in the Democratic Presidential primaries
In the Democratic Presidential primaries, the superdelegates are long time Democratic insiders whose vote make up one third of the delegate vote, with the remaining two thirds by the people. Of course the superdelegates are grossly biased toward insiders like themselves. Just comparing the popular vote in the Democratic primary, Hillary Clinton won 15.8 million votes (56.8%) vs Bernie Sanders who won 12.0 million votes (43.2%). It would have been very likely that Bernie Sanders, who is far more respectable, likeable, trusted, and popular (his rallies draw tens of thousands of people), could have won if his momentum was not suppressed by the superdelegates.