If talking a fantasy setting I would do the following
- Using one page sketch a world or continent map
- Label important regions
- Write one page of background giving no more than a handful of sentences to each region.
- Pick an area roughly 200 miles by 150 miles
- Grab a 8.5 by 11 sheet of hex paper.
- The scale should be so that it represents a 200 by 150 mile region
- Draw in mountains
- Draw in rivers
- Draw in hills using them to divide the region into distinct river valley
- Draw in vegetation (swamps, forests, desert, etc)
- Decide to place Population Locales note their race this includes social monsters
- Decide to place Lairs (locales tht revolves around a home of monsters)
- Decide to place Ruins (locales that revolves around a site)
- Decide to place miscellaneous locales. (anything that doesn't fit a above.
- Name your geography (don't forget islands)
- Write a Half Page background describing the region and it's history.
- Write a paragraph describing each named geography
- Write a paragraph describing each Population Locale
- Write a paragraph describing each Lair (you could get away with a stat block)
- Write a paragraph describing each Ruin
- Look at your notes and come up with two to four plots that ties one or more locales together. Write a paragraph or two on each.
- For each population locale come up with three to five encounters. They should be a sentence each.
- Come up with 6 to 12 general encounter for the region as a whole. Should usable in any area of the region. They are a sentence or two each.
- Pick the 4 or 6 most important Population locales and draw a quarter page sketch map of the settlement.
- Pick the starting population locale and draw a full page map of the settlement. This is the "Home Base"
- Use Medieval Demographics to get an a idea of how many shops are in the town.
- Pick or create 6 or 12 important buildings. Write a paragraph each.
- Scan your descriptions for NPCs or noted monsters. Write a two sentence about each. The first a one line with minimal stats the second one sentence. This is your roster.
- Pick the 12 most important NPC or Monsters
- Write a paragraph describing each and fully stat them.
- Pick the most six common encounter type. (City Guard, Border Warders, Bloody Hand, Orcs) Write a paragraph and fully stat them.
- Scan your description for any regional organization and write a paragraph on them. Fully stat the most common encounters involved with them.
- Make up a rumor chart with 10 to 20 items that feeds the players into the encounter and plots you created in above.
- Identify major regions and create a random encounter chart for each (monsters, wildlife and NPCs) [Thanks Jeff I just plumb forgot]
This will probably run to about 10,000 words. You can do this in about 2 weeks spending about 2 hours an evening at a 1,000 words a evening and time drawing maps. Or consider it about 24 hours of work.
This is being expanded in the following posts.
A Fantasy Sandbox in detail Part I covers Step 1
A Fantasy Sandbox in detail Part II covers Step 2,3, & 4
A Fantasy Sandbox in detail Part III covers Step 5,6,7,8,9, & 10
A Fantasy Sandbox in detail Part IV covers Step 11, 12, & 13.
A Fantasy Sandbox in detail Part V covers Step 14, & 15.
A Fantasy Sandbox in detail Part VI covers Step 16.
A Fantasy Sandbox in detail Part VII covers Step 17.
A Fantasy Sandbox in detail Part VIII covers Step 18, 19, & 20.
A Fantasy Sandbox in detail Part IX covers Step 21
A Fantasy Sandbox in detail Part X covers Step 22
A Fantasy Sandbox in detail Part XI covers Step 23
A Fantasy Sandbox in detail Part XII covers part of Step 24
A Fantasy Sandbox in detail Part XIII covers part of Step 24
A Fantasy Sandbox in detail Part XIV covers part of Step 24
A Fantasy Sandbox in detail Part XV covers part of Step 24
A Fantasy Sandbox in detail Part XVI covers part of Step 24
A Fantasy Sandbox in detail Part XVII covers Step 25
A Fantasy Sandbox in detail Part XVIII covers Step 26
How to Make a Fantasy Sandbox by Robert Conley with layout by Patrick Walsh. (Bugbears for Breakfast)
collects the previous steps into a single PDF.