I agree with the above from Lasttrainintolondon.
Focus is needed on a small number of big issues and aim for centre ground (that is what new labour did and they were the last labour government to win, and they won more than once).
I would suggest the NHS and education.
Under Tony Blair, there were waiting time initiatives, by the end of the last Labour government the 4 hour A&E waiting times were being met almost all the time, cancer referral times were being met.
This is what people want now.
Look at the outrage from those who can't get a GP appointment, have a 18 month wait for surgery, 12 hours in A&E etc.
I would suggest KS and AR could remind people that the first health policy of the new Tory government that took over from Labour was to remove all the waiting time targets. Even before the pandemic the waiting times were dreadful and unpopular.
Labour need to play less nice. The vast majority of the GBP believe in the NHS and state education, neither of which the Tories really value (Jeremy Hunt wrote a book about how to dismantle the NHS before being appointed health secretary, most of them are privately educated).
They need to be prepared for a rehash of Theresa May's magic money tree infantilised dumbed down argument.
(e.g. a few less billions in contracts for mates would be a lot more money in the public sector)
But labour did it before with the NHS and they can do it again - that is what the argument should be.
Sleaze is difficult to focus on. I think part of the appeal of Johnson and his government is that it makes people feel better about their own lives, mistakes, cash-in-hand tax dodiging etc. They can relate to Johnson's shoddy morals and mates-rates culture and it legitimises some things about their lives. I think there is a large proportion of the electorate who wouldn't turn against the government for sleaze because sleaze doesn't bother them in other arenas of their lives.