This is incomplete, and focuses on (a) the real basics and (b) the Grand Campaign. I plan to add sections on moderate power campaigns and using the background material next.
Comments and criticisms invited.
The Beginners' GUide to GMing Harn -- first draft
This guide assumes (a) you've GMed fantasy games before, but are new to Harn and (b) you own only the basic HarnWorld regional module. You've probably read it and been thinking, "Wow, great detail, but where are the adventures? How do I turn this into something I can use in my games?" These are the questions we hope to answer. We do not assume you will be using the HarnMaster rules, or any other specific set of rules; we aim to give generic advice.
The first thing to understand is that Harn is written with a subtle touch. Numerous adventure possibilities are hinted at within the source material, but few are made obvious, they don't seem to affect ordinary life in Harn and most seem to be held "in abeyance". This brings us to the second important point: the writers and publishers of Harn have made a commitment that they will never publish official material which takes Harn beyond the default starting date of 720TR.
This has a couple of major effects. Harn requires your creative input as GM to turn it into a living, breathing FRP world; you can run pretty much any kind of adventure or campaign you want in Harn; and once you've started the campaign clock ticking, you don't have to worry that some future publication will supercede your own invention.
There's a common misconception that Harn is a low-fantasy world. It isn't. Harn has as many high-fantasy elements as it does low-fantasy elements. It has detailed feudal societies, and it has dragons. It has medieval crop rotation systems, and it has a god, and at least one demi-god, living on the island. Whether your Harn is low-fantasy or high-fantasy is simply a matter of what you choose to emphasise; Harn itself is flexible. The 'default' level in the published material tends to emphasise the low-fnatasy elements because it's much easier for you to add the high-fantasy elements you want then it would be for you to remove them were high-fantasy the default and you wanted to play a low-fantasy game.
Before we plunge headlong into finding adventures, let's consider one last general point: Harn doesn't seem to have a place for the general adventuring party. There are no adventurers' outfitting shops, definitely no magic shops, and there don't seem to be any "adventuring parties" among the background PCs. This is true. Fighters, thieves, clerics and wizards seem to lead very different lives on Harn, so it's rare they come together, but that doesn't mean it can't happen. If your players want to play diverse character types, you can accomodate them easily enough -- and a little time spent thinking about how this unusual band came together may well reward you with some adventure ideas.
Finding the adventures in Harn is really just a matter of getting your eye in (or acquiring the mind-set). It goes without saying that you can run any number of generic FRP stock adventures -- rescue the missing person, find the mystical doo-dad, save the village from attackers and so on -- but here we're concerned about finding specifically Harnic adventures.
The way I do this is to read the source material. When I come across something that catches my interest, I make a note of it (you can use a notebook, or a post-it sticker attached to the relevant page, or just make a mental note). I let these interesting items percolate round my brain for a bit, considering possible ways to use them, and the ones that strike me as particularly fruitful I develop into fully-fledged scenarios. I call these three stages "A-ha!", "What if..." and "The game's afoot!".
I'll give an example: flicking through HarnWorld, we find some pages of introduction on the topography, and cultures of Harn, soem notes on government, rural life and town life. All of this is good background, but hardly the stuff of adventure. There's some stuff on guilds, religions (we're keeping reading the Harn article, not digressing into Kethira or Lythia -- that odd organisation is because Harn's designed so you can cut it up and organise it into folders; some people do, others don't). Hmmm... the kethiran family? Planar travel is an option, then. Let's save that for later. Aha! Mysterious Ancient Race (Harn 21). Ancient artifacts... godstones... scattered ruins... this has potential. It's a little too grand in scale for the opening of a campaign, though, so I make a note and move on (maybe the campaign will turn out to be to do with the Earthmasters eventually, but not yet...), arrival of the elves, dwarves, humans, founding of Melderyn... hang on, it says here that Medleryn has exerted little *obvious* influence on Harn. It doesn't say no influence. Why the qualification? Perhaps there's something covert going on here... that's got potential. Hmmm... Wizards' Isle, occasional visits to the mainland... there's definitely something going on. Let's backtrack a moment -- on the previous page it says some people believe the Earthmasters never left, but withdrew to Melderyn where their descendants live to this day... an idea for a campaign is beginnign to form.
Let's read on: Lothrim the Foulspawner -- hmm, renegade mage from Melderyn (there's those magi again). Hmmm... Lothrim chose an Earthmaster site for his capital... imported the gargun... riegn of terror... Kills every dwarf in Kiraz (note to self: we have a deserted dwarven city out there... Moria, anyone?)... hmmm, Lothrim cast alive into tomb with a dozen starving gargun -- it doesn't actually say he died, does it?
Let's take this Earthmaster/Melderyn/Lothrim thing and move to the "What if..." What if Lothrim was really one of the good guys... that would make these mysterious magi, possibly descended from the Earthmasters, the bad guys, right? And, whatever happened to Lothrim, these mysterious magi are still around, pulling their strings in the background like the Illuminati of old... we need to know more, though, so let's look up "Melderyn" in HarnDex. One of the first things we find is mention of real power being held, not by the king, but a group known as the "Council of Eleven", a msyterious body of scholars... perhaps these are our mysterious Illuminati. It says they have a benign influence on Harn -- but we want them to be bad guys. Well, history's written by the victors, isn't it? Perhaps they just want you to think they're benign...
This has the potential for a really grand campaign. We've blended several story arcs (the Earthmasters, Lothrim, the Council of Eleven) into a big conspiracy theory. There's a long way to go -- we don't know what the Council is really up to, for instance, and we haven't yet got any idea how to turn this into specific adventures, but those are details. A little work and they'll come to fruition. We know our campaign is going to involve exploring Earthmaster ruins, finding Earthmaster artifacts, working out what really happened to Lothrim (and why), and that the party will be opposed by mysterious magi from Melderyn. The backbone structure of the campaign is in place.