Quite a number of economists would argue that high national debt is not infact the key issue. That the people who think it is are either deliberately inflaming the issue for political reasons or don't understand the difference between personal debt and national debt.
Stimulating growth in the economy by investing in employment both by investing directly in jobs by for example investing in infrastructure and by reducing the barriers to employment by for example subsidising things essential to employment like transport and childcare will ultimately lead to a stable economy and less debt.
Reducing benefits is tinkering round the edges until you do this, if you cut the benefits of your 500,000 unemployed families but add another 200000 unemployed families this year your bill is obviously not going to reduce. More means testing is catering to jealousy and votes but will do nothing for the economy, means testing is expensive.
Closing tax loopholes is definitely a good idea but increasing taxes for the rich is not going to help the economy, it is also catering to jealousy and votes just from a different section of people. You want people with ridiculous amounts of money to spend it on things. You also want your poor to have more money and since they contribute less tax through income anyway, your best way to increase your tax revenue is to reduce their tax rate, increase their personal allowance so they have more money and spend it on goods increasing VAT revenue.
The problem with the economy is not the national debt, it is the fact that it is managed by politicians not economists.