First and foremost being in a position to enact change.
It might not be every change you want, but that is because you hold an idealised rather than a pragmatic view of how politics functions.
The first part Is almost true imo.
But before even getting into power a Party should have an agreed, fully thought out idea of what it wants to achieve rather than just letting the electorate in on it after the election. The public deserves to be told exactly what they are being asked to vote for rather than just be considered as crosses on ballot cards.
I agree with the earlier comments you made about Corbyn being a hindrance to Labour's electoral prospects, but so far Starmer's main achievement has been to show who he is not i.e. Corbyn/Johnson, while trying to show he can match Sunak for fiscal responsibility. All of those were good tactics especially as the Tories seem intent on self-destruction and they have worked so far, but I sense some cynicism creeping into the electorate about whether Starmer is actually just the least worst option.
There is a reasonably long time before the next GE and he has time to show that he has some policies to offer that one would expect of a social democratic party, as it is clear that the term Socialism is not the vote winner that some in the party think it should be. I hope that he does this but does not continue to try to be all things to all people e.g. the mixed message of "
Rising child poverty is a chronic injustice that scars society" from the Future for Families document, while tacitly supporting the two-child benefit cap that exacerbates child poverty.