Hey, knock yourself out. I'm always glad to help. :)
If you're thinking of a town in the middle of an open landscape, well, the quickest reason for a town there that I can think of is a cross-roads from several regions that developed into a trading area. Naturally, local farmers would also start going there to trade their produce for other goods and soon you have a more-or-less thriving little town. Next thing you have to pay attention to is whether this is more of a frontier town (i.e. has walls and is limited in area) or if the town is in a relatively safe area. If the area is safe, the town will sprawl, since a flat, fertile, open landscape means people won't need to be crammed together and even some townsfolk will often have plots of land for producing vegetables and other food-stuffs. In this case, you'll have the town mingling almost imperceptibly into the countryside, the houses get spaced further apart, you start to find aristocratic manors, mills and other things.
Now, if this was an open landscape, a natural second thing that would bring local farmers to the town would be the construction of a big windmill, or, heck, a magical earth elemental powered mill, if it's a magical setting. Once you have a market and a mill, the town naturally becomes the focus of the surrounding countryside, and as a crossroads, it becomes a stop-over for traders from different regions, giving you at least a tavern, an inn, stables.
After that, if it keeps growing, you get craftsmen and artisans settling down there to produce goods, though primarily those that don't require a lot of water to produce (water wheels and water were the main source of power after the water wheel was developed in the middle ages) - so probably no tanneries - but you could have carpenters, shoemakers, smiths, weavers, tailors, jewelers, etc. depending on what was being traded in the town. Once you have craftsmen, you start getting guilds, and those pretty soon start showing off their wealth and helping finance a nicer temple or two, after a temple you might get a small monastery and buildings for the clergy appearing.
As the town grows, you need a town hall for administration, probably a town watch building and small prison, maybe a watch tower (to watch for fires, if nothing else!). You will probably get at least 1 building for the sherriff or whoever it is that represents the state government in the town (unless it's an independent polis). You also start getting civic areas for celebrations, like plazas, statues, more market areas ...