I think that the first thing to do would be to decide why that guild/faction exists. If its something like a thieves guild, then their main goal should be to facilitate the stable income of their members, and everything else would be built around that. They wouldn't really have a reason to fight anyone else, unless it was the guards or some other thieves guild encroaching on their territory. On the other hand, if two factions were dramatically opposed, like a good aligned church and a sect of demon worshipping cultists, then they should have clearly defined boundaries to keep them from fighting, with skirmishes often breaking out. Ex, cultists are too well hidden for the church to just march in and wipe them out, but paladins are constantly searching for and eliminating their hideouts. Think about it from the leader's point of view too. If two kingdoms that hate each other are equally matched, logically consider how much that the rulers would be willing to invest in opposing each other. If starting a war would mean famine and economic collapse, then there probably wouldn't be war. Unless your king/tyrant/ruling council are crazy. Then you can pretty much do whatever you want.
Generally though, guilds are much more free form, with each member joining for their own benefit. Other types of factions are much more tightly knit, with Orders and Sects often having some sort of overarching philosophy or trait that ties it together. Clans work for the benefit of the family, and Churches serve their gods. Nations serve the ruler, which is often more than just one person, since even a king needs the support of nobles/army/influential people.
