To tell the truth, not too different than what he's doing now. The idea that he could somehow be dominating--or even be a big part of--the national conversation if he was a stronger candidate is far-fetched. And it's actually fine that he isn't. Amy Walter gets this exactly right.
"[T]he hand-wringing from some in Democratic circles that Biden needs to ramp up his public presence, lest he be 'forgotten' or overshadowed by Democratic Governors like Andrew Cuomo or Gretchen Whitmer, is unnecessary and misses the point.
First and foremost, in a national crisis, the attention is trained on the person in charge and not the person who wants to replace him or her. This scenario works to Biden's benefit. Even before this horrible virus hit the United States, Biden's best opportunity to win in November was dependent on making the contest a referendum on Trump...
Then there's the other, seemingly endless worry by Democrats that Biden fails to motivate Democrats. The most recent Washington Post/ABC News poll gave this theory new oxygen...Almost immediately came the comparisons to the 2016 Hillary Clinton campaign... But, this isn't 2016. A Trump presidency isn't a theory; it's the reality. In 2016, the only reality people had was the last eight years of Obama and the very well-known history of the Clintons.
More important, Biden's goal isn't to be a more 'exciting' alternative to Trump but to be the opposite of Trump. Biden isn't going to be a ratings superhero. He's not going to pack stadiums to the rafters with supporters. His message is basically this: I'm pretty boring but steady and competent. That may not work every year, but it is well-suited for a time of chaos and confusion.
It's also important to put the 'enthusiasm gap' into perspective. Trump was successful in 2016 not just because he had an energized group of voters supporting him (and turned out people who had been on the sidelines in previous presidential elections), but because he won a disproportionate number of voters who disliked both him and Clinton. In looking through the 2016 exit polls, CNN found that "voters who held their nose in the voting booth appear to have preferred someone new over someone who had been in politics for decades. Among this disaffected group, 44% favored change, while only 13% prioritized experience." Today, government experience is unlikely to be seen as negatively as it was four years ago."
In short, for Biden and the Democrats, the best possible way for the November election to be fought is as a referendum on Trump. That was always the biggest problem with Sanders--it was easy to envision the election becoming a referendum on Sanders not Trump. The current situation, despite Biden being on the sidelines, is evolving toward what the Democrats want and need-- a Trump referendum election.