Sandbox structure is fun. I enjoy it in principle and have really enjoyed building the world that my players are begining to explore. I know there’s a milion of these on the web, but I figured I’d throw up the pitfalls I have hit and things I have grokked from my own experience and from a game design perspective.
1. Give them some starting MacGuffins.
This has been stated several times in several other places, but dont just sit down with your players, tell them theres a forest outside town and ask what they do. Create a rumor list, or a bounty board, or a job board in their home base/town. Hell do all three… Be a kind and benevolent GM and give them a purpose. Once they have burned through that info they likely wont need any more prompting because you should be seeding your points of interest with clues and directions to other sites.
You really should only need to populate the specific “quest NPC’s” once, doing it more than that makes town the quest depot when it’s more desireable (imo at least) to have the players discover and share the info that they find Out There. That said if you want to use the town as a quest depot in a more structured environment there is no reason not to.
2. Build more than you think you will need.
If you allow players to wander anywhere, and you let them get lost, trust me, they WILL wander out of the areas you have planned. Make sure those Encounter tables are all nice and padded out, or that you are comfortable winging it.
3. Link the points of interest together somehow.
All of my sites have clues to 2-3 other sites. These arent flat out directions, but they should give the players a good set of information, especially combined with info found elsewhere. This will allow them to put the puzzle pieces together to explore and find the locations without you holding their hand and having the old guy with the glowing eyes in the corner of the tavern point them at everything. This should act as a great carrot on a stick and motivate the groups to get out there and explore.