For example, here's an idea that would make the ineffective UN immediately more effective. This took me about five seconds to think of as an idea.
One problem is the inherent source of much conflict in the world, which are civil wars, internal to a country and/or neighboring countries who have ethnic groups that cross boundaries. However, the way the UN is structured, whoever rules the government of each country appoints the ambassador to the UN. Do you see an immediate problem? That has plagued the UN from day one.
My suggestion is that in addition to appointing the official ambassador to the UN, each country must send a delegate as an observer and a participant on committees and so forth from the minority party, the party in opposition, or the next largest ethnic group in that country. For example, when the Dems are in power in the USA, the Reps get to select a shadow ambassador. Hopefully the two would provide valuable common ground in their time together. As another example, a Muslim country with both Shia and Sunni would appoint one as the official ambassador according to how power is held in that country, and the clerics or other leaders of the minority denomination would select their shadow ambassador.
This would be crucial whenever any civil conflict arises in a member nation and/or when there is cross boundary tension between two groups struggling for power. One would be the official ambassador to the UN, per the country's rules for determining such, and the other would be the valued educational and awareness ambassador, working with the official ambassador and also representing his or her group's interests to the UN at large, separate from specifically that country.
How cool would that be? And actually useful.