The UN should be drastically reformed in three major ways:
(a) the Security Council system as it is is abolished. A new, permenent security council is enacted with no veto powers for any parties. The 15 nations comprising it should be as follows (America, Britain, Germany, France, Russia, Brazil, India, China, South Africa, Nigeria, Japan, Australia, South Korea, Turkey/Pakistan/Egypt and Mexico).
(b) the UN should cease peacekeeping activities as an organization and contract them out to regional organizations (African Union, Arab League, EU, NATO, OAS, ASEAN) which willl have the option of flying under the UN flag or not. This way, there is no shortchanging of the peacekeeping operations by donor countries or volunteer countries who contribute troops only to get money and acclaim)
(c) Automatic triggers will be built into key emergencies like genocide, nuclear proliferation and oppressive invasion. This way, no nation like China or France will be able to discredit the system by making deals and stalling for time for oppressive regimes like Sudan, Iran, North Korea, Burma, etc etc.
I don't know, there are lots of other ideas, but these are the ones that appear most possible (still improbable though sadly)