Taxes should be as simple as humanly possible, both for the individual to understand and the state to enforce.

The UK has a hideous system. The biggest recent tinkerer was dear old Gordon, but he's not alone.

Everyone should start off being theoretically paid a sum of money. If you earn nothing this is pretty much all you get. You'd be very limited to where you can live and your disposable income is close to zero. You probably won't have enough money to have kids. Want to prosper? Do some work.
There is certainly no unemployment allowance. Everyone is effectively paid that - and we can scrap all the infrastructure that is employed in doling it out and ensuring people get the right amount. Want to work? Great. Go to a recruitment agency or online.
Then there is a period where tax is zero. Earning is always worthwhile. The most menial jobs mean you earn that much more money.
Then you collate all money that is coming in from basically all sources and whack it into a calculation that taxes on a slowly increasing scale.

No nasty jumps where earning more can mean getting less
No cunning "earn little and then get the money as dividends from your own company" crap. If you get the money you sum it up.

Very simple to instigate.
No complex forms to complete to work out what exactly one is going to get. The cost of instigating and sorting out the system would be a lot less.
No "incentives" not to work as the benefits lost are greater than the money earned. No U shape where people get stuck as to bother isn't worth it.
A hell of a lot less bureaucracy at the other end.

Needs fine tuning? I'm sure. The payment to everyone would have to be monthly as those that need it both will generally be poor at budgeting and not be able to wait until the end of the year.

There are few countries that need such a radical overhaul. With clarity it will be a lot easier to see how exactly to go about balancing the budget.