By using a powerful virus, I will infect all the world's networks to hold the world ransom, unless they want every digital technology to shut down or go terminator.
My demands are difficult, but nothing terrible. I want modern government abolished, everywhere. It needs restructuring, and a possible apocalypse is a good enough motivator, might as well do it in one swoop. The nations of the world will be free to re-elect their own politicians - NEW ones - to fill spaces in a reformed government. I myself will oversee the process and reserve the right to veto the results should it appear corrupt or unfit. In fairness, I reserve no position of power for myself.
The world will gain a global currency. Specifics of appearance are free to vary by nation as they do now, but values are universal. Money is to additionally be used as a reward system, when possible. Or, in most cases, helping those in need will be a situation where costs are neglected. Seriously, money has a purpose, but it should never take priority to human life.
Funds will be distributed to the poor and needy. Given that finance is receiving a large change anyway, a second start for these people is not difficult. Along this vein, the use of money from taxes will be displayed to all, as will the restructured laws (which will be intended to be clear and with minimal-to-no room for interpretation). Each expenditure has a limit of tax money available, any excess must be obtained by other means. Changes to these limits must be voted upon.
Major issues are to take public opinion seriously. Freedom is of highest priority to those in charge, but any issue that would breach any human freedom MUST pass a public vote by a notable margin.
Finally: War. If it is to occur, those who issue the commands or instigate the war must fight with the troops. If what you're after is so damned important that you're prepared to send hundreds to thousands to their deaths, you must be willing to do the same with yourself.
Ahh, that was fun. I like this question.