This is obviously not a full guide, but just a little article to help you choose your perfect area rug. Here, in this article we just combined a few things to consider when making a decision about your area rug.
Always look to reach contrast between the rug and your floor
First of all: SIZE. Yes, most important thing, size. You need to measure up your space - while this applies to any furniture purchase, it is most important to area rug choosing process as well. Typically, in US, there is 2 most common sizes, 5 x 7 or 8 x 11 (or 10). While bigger rug is great choice almost every time - it's not particularly true in all situations. In smaller rooms or smaller areas bigger rug could look out of the place, going under furniture too much or gets 'eaten' by your huge sectional, etc. When choosing area rug - place something on the floor, like glasses or anything else to measure the limits of the rug and see how it will locate. It will help.
Thicker area rugs would work magic on hardwood floors
Rug color, pattern. A very simple rule applies here: rug looks way better if it's contrasting to 1) your floor/carpet overall color and/or 2) to your furniture color. It seems obvious but a lot of folks forget about it. Yes, different things in decor look better together. If your floor is light, choose a darker area rug and vice versa. Same applies to furniture. One more important thing to consider: if furniture is relatively plain, it would be better to choose an area rug with some definitive pattern. And vice versa, of course.
Distressed area rugs is very nice dramatic touch to your room design
Consider where rug is going to. Hardwood floors are the best, but carpets would work as well. When choosing a rug for your carpet you need to consider twice - first see color options (drastically different is better) and secondly, thickness. Obviously, a thick rug would look and feel better on a floor than on the carpet.