A slightly more didactic topic, I came upon a fantastic article that cleanly summarizes the basic theory behind graphic designs (more specifically the nature and characteristics of a good logo)
The original article can be seen here:
http://justcreative.com/2009/07/27/what-makes-a-good-logo/
This website explores that the composition of a good logo is often comprised of 5 different characteristics:
1. Simple
2. Memorable
3. Timeless
4. Versatile
5. Appropriate
Simple - to summarize what the article describes, a good logo is often characterized by qualities that are clean and neat. Yet, they are capable of expressing the company/ group's name with elegance. Consider this as an introduction into "Minimalism" theory or beliefs, because this quality essentially goes hand-in-hand with keeping a logo simple.
Memorable - a memorable logo is characterized with qualities that are easily recognizable. These are essentially capable of taking any form, and the viewer or audience will still be able to see the original logo made.
Timeless - A logo that is timeless will be capable of withstanding the tribulations of time. A logo that is timeless will hold its symbol into eternity for future generations to view. Essentially a quality of being culturally durable that would allow it to span the mercurial nature of social fads.
Versatile - Being versatile basically means: "will this logo work across a large spectrum of mediums?" A logo capable of changing from one medium into another is the basis that defines versatile symbols.
Appropriate - Is the logo appropriate for the purpose that it's serving? For example, a logo for a beer company wouldn't use bright colors reminiscent of childish activities, nor would a children's brand label use racy and sexually tense images to advertise products. It simply isn't appropriate.
I didn't expound deeply into the subject, however, the website has more information if you'd like to know more. It's also brilliant because it gives other resources for you if you want to know even more!
(all logos viewed in this post do not belong to me, nor am I affiliated with their respective owner. Credits belong to their respective owner who owns copyright.)