Well, GrannyRose15, it's taken the tories 13 years to break the UK so I don't think there are going to be any quick fixes.
They could boost the economy quite fast by sorting out public service pay as most of the money would be spent into the economy, giving a boost to all the private enterprises that would be supported by consumers actually having enough money to spend in them.
And putting money into public services, such as the environment agency would help to stem the pollution of our seas and rivers. HMRC would be able to chase up the big tax evaders more effectively. Social care, the justice system, the NHS(and doubtless other services which people could name) would all benefit from some state investment.
But the big problem they are going to face is a shortage of trained personnel for these services as training is a long term issue. We're going to have to rely on immigration to help solve this problem in the short term and possibly in the long term as the population ages even further and, at the average family being 1.7 children, it's not being replaced
Then there is the Green agenda, more investment in retrofitting old properties to make them energy efficient and investment in alternative energy. They've already signalled investment of £28billion, though it would take much more than that.
The NHS needs a thorough reform to make it an integrated care service and to cut out the silly business models that the tories introduced which just make patient care much more complex. It needs careful thought and planning and isn't going to happen overnight.
Then, of course, the UK has to be somehow rescued from the ridiculous Brexit decision...
I think it will take at least two terms and a lot of money to get the UK on its feet again.
This is just off the top of my head.
Truthfully I am a bit doubtful as to whether Labour has the necessary vision to make the much needed huge initial investment, but I can hope...