Try this site:
http://adndology.co.nr/
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GM Discussion > house rules
for some ideas. Also this is an excellent resource for gaming ideas in general. (You only need to register to post.)
As for myself, I have been running D&D for 20+ years. I prefer to create a scenario in only the vaguest terms.
1) write out the major NPCs (name, class, level, alignment.)
Is he in charge of an organization? (Name, size, general structure, command style...)
2) Create in detail the NPCs the players will actually encounter. These ones generally get the full treatment. (name, class, level, alignment, proficiencies/skills, items, spells...etc. in short, treat them like a normal pc under your control)
3) The better you know the environment, the scenario, and the factions, the better.
4) introduce the PCs to some element of the scenario. When they intervene, have the factions involved respond in the most rational, realistic manner possible.
For example, the PCs could stumble across a kidnapping. This might lead them (with a little investigating on their part) to the existence of a crime ring. viola! the campaign is afoot!
This method does not depend on a L-G party alignment. For instance, in the above example, there is nothing to stop them from extorting the crime ring or ignoring their activities altogether. Just be prepared to re-introduce the story. Once. If the players are not interested, have something else ready.
In this event, I would suggest something simple, and generic. A little orc-bashing can sometimes go along way.