[PF/3.X] Seeking tips on solo adventure/campaign

[The Insanity]

When running or designing an adventure/campaign for just one player, what are the things that you should keep in mind or watch out for? Any tips for DMs?
Conversely, when playing such an adventure/campaign as the player, what good ways are there for building your character, with the assumption that the DM will adjust the plot to be at least a little more <insert your PC's build here> friendly? And without the aforementioned assumption?
I've seen some solo games in the Recruitment board, so I assume it's not that rare. If you played/DMed a solo game, how do you do it?

[ArcturusV]

I've DMed a few. The keys I found for it:

1) Competent World. I think this is the key one. Most campaign worlds seem to be based on the theory that basically everyone has their thumb up their butt, and is barely capable of figuring out how to feed themselves without the player's doing something. Or at least that's the feeling you get as you're asked to solve pretty much every problem with just your group of heroes, on your own, etc.

In a solo campaign though I feel it's more important that the world around you shows some sign of being decent enough at their jobs. This is for several reasons. Chief being "It is dangerous to go alone". A group can be told "Go kill that goblin warcamp on your own" and have a decent enough chance at victory based on how the game is written and it's broken down.

Solo, unless you're high level (Which I admit I almost never DM), that's pretty much impossible. So you presume that your locals are somewhat competent. Thus the mission changes from "Wipe out an entire goblin warcamp on your own" to something like "Okay, we're launching diversionary raids here, here, and here. We can keep the goblins busy for a short time before their sheer numbers start to overwhelm us. During that time you need to sneak in and wipe out their leadership/swipe the MacGuffin/rescue hostages/etc". This not only adds a pressure clock to the thing, but it also provides reasons for the player to have a chance in hell at soloing it. And the possibility that if things are going bad they might try to run to one of the Raiding Parties for reinforcements and escape.

2) Setting their own pace.

Generally... I'm LOATHE to let players determine the pace of encounters. Because you end up with this stuttering style of gameplay, and the tendency for "Narcoleptic Adventurers" where they are only awake for 30 minutes, blow their wad, then sleep for 8 hours. But they kind of need that advantage with a solo campaign. At the very least they need to feel like, if something goes wrong, they can leave, rest, recover, get items they might need, etc, and come back without it being a complete screw job. It's just one guy, so he's less likely to have the answer to any problem on hand. So let them run a single encounter, have a hard time, and go "Oh ****..." and run back to town to beg the clerics for some Holy Water, or research some spell that will help them solve their problem, etc, etc, etc.

3) Letting the Rule of Cool be.

Just what it says on the tin. Oftentimes with a group I'll be worried about one guy becoming the "Rockstar" and the group dynamic suffering because everyone else feels like back up in their own game/story. Not a problem with a solo campaign. I also let stuff that isn't RAW/RAI slide just because... hey... why not? For example solo game with a Rogue, he went and fought Undead.. and decided to try to use Holy Water to "poison" his dagger in order to sneak attack undead. Not RAW or RAI at all... but hell, why not? It was a neat enough idea. It let him have the power he needed to more easily deal with the undead. Let it go.