James' Quick & Easy 7 Step List
1. Find people that wish to play, make sure that they can all show up at/around the same time.
2. Create X amount of NPCs, alternating good, then bad, then someone in between.
3. Create 3 or 4 countries, and make sure there is a bit of everything geographically. Steal a map from somewhere if you have little time.
4. Give all the bad guys power. Evil minions, trap-filled dungeons to hide things, rituals to summon world ending baddies, whatever you think they can use. Then give good guys a lot less personal power, but more political power.
5. Have all NPCs oppose each other in the world, but they 'balance' each other out.
6. Create adventure hooks that the party can use to upset this world balance. Give party ample room and power to screw up anyone they feel like.
7. Start the game, preferably by creating a small town that the party can do mini-adventures and hear rumors of various NPCs.
At this point, every week you add more to the game in your off-time. If the party is exploring, add more cities, towns, ruins, and dungeons to your map with a short write up. If the party is going hacking, get a dungeon together. Just keep ahead of the party by asking what they plan on doing from week to week. The game will build itself.