In a 1 shot I tend to expect that they will incorporate the goal of the 1 shot as their goal. My current 1 shot is stealing the MCguffin from the wizard king's vault. This is to give the other DM time to finish up the details for his more sandbox style campaign.
Okay, so with a one shot, things may be a bit different, because things are going to be more constrained. I was thinking of more sandbox or open world play when I was picturing flowcharts, but let's see what we can come up with.
So if we were to break things out as a flowchart for this scenario, how would it look? I expect that there's a base location of some kind, and of course there's the wizard king's castle, and his vault. So maybe those are three boxes on the flowchart. So how do we move from one to the other?
Are the PCs hired to steal the maguffin? Is in something of personal interest? How do they know about it?
What makes them move from the base location to the wizard king's castle?
Again, the answers to these questions may be incredibly obvious for one shot that has such a specific goal, but maybe the above helped explain what I'm talking about.
In a sandbox style campaign, there might be some high level initial goal but they are ultimately free to move away from that anytime they want. I guess that's the biggest thing about this kind of sandbox, they make their own goals.
Based on what? Surely there has to be some structure in place in order for them to base their goals, no?
So if the goals might be to accrue wealth and magic relics (a pretty classic motivation) then that likely means that there is treasure to be had, right? Which implies a geographical map with locations that may offer treasure of some sort.
So, again to kind of view this is a flowchart.....there's likely a home base town as the starting point, with a few options for potential treasure hunting as other boxes in the flowchart. Things like "the ruined temple" and "the cave of the lizardfolk" and "the dungeon of lunacy" and so on.
Now, these boxes need not be set ahead of time, but I'm kind of assuming that's the case based on what folks have been saying about the sandbox style. They could just as easily be generated procedurally through random charts and the like. They could just as easily be crafted according to actions declared by the players. There are multiple ways to do it, but let's go with "GM creates the setting prior to the start of play".
So you have these locations and they're there for the PCs to engage with.
How does that engagement get facilitated? Do they need to explore the map and find one at random? Are there NPCs who offer clues or suggestions about the locations?
What do you do as a GM to help the players set their goals and then what do you do to help them try and achieve those goals?