One of the problems with most fantasy worlds is that they are not places you want to live in. Beyond the usual hygiene issues, the problem is that they were set up in a rush with more worries for literary issues than anything else. Because of this it may help to take a step backwards and look at the world in general.
The first point to look at is whether you need to look at in micro or macro. Looking at the world in macro is a pretty good idea if you are doing something epic or legendary; you need to know how the world works as a whole before you make major changes in it. On the other hand, it helps to look the smaller details if you writing a coming of age story or something personal. If you are looking at in micro, all you need to establish is where the food comes from, what the hierarchy the person needs to worry, and what the person does for a living. It really is that simple, but you will also have limited range of stories to worry about as well.
Let’s look at the micro view for a moment. If you are just interested in a limited story, you need to avoid nobles and any military above the rank of company captain. Nobles do not work for small stories, especially if it’s a fantasy world; they are just too rare and therefore important to how the world works so they cannot be used in small stories. The higher the rank of the noble, the more you need to have a story that uses him. This is why Disney princesses are usually involved in major stories; if you are going to use someone that rare you simply don’t waste that person’s presence in a small story. The same applies to any high-ranking military officer; the scope of their command usually justifies a much greater role. This is not to say you can’t use them in small stories, just realize that it may come off as strange; you wouldn’t send a hero of the realm to go after a small minnow, after all.
You also need to establish where the food comes from. It may sound trivial, but in a medieval environment that will an extremely important detail. Even if it’s just fish or grain it is important to establish that there is a food source. If you don’t, then you establish that there is some sort of famine, and that’s just as important. Either way you establish something important about your environment. You also need to establish what job the characters have as that also adds to environment, especially given the difference between status level when it comes to things like who gets priority when it comes to protection, food, or decent living quarters.
In short, you need to establish just enough that it’s a real world. And this level of detail is required just to make a short story. Imagine the level of detail you’re going to need for something bigger…