I studied graphic design for about two semesters at college and the main piece of advice I'd offer to potential graphic designers is do not confuse it with art. It's a highly creative profession, that's for certain, but you are by no means allowed to just run free and make whatever you think looks good. Graphic design schools try to beat this into you from day one by forcing you to explain why your design is effective; in the example of a logo design, you have to have reasons for your choice of font, color scheme and any other graphic elements you might choose to include. It also has to fit the guidelines of the project and be consistent with what the logo is going to represent.
Graphic design informs much of the symbols that surround us in the modern world and in order to be successful as a graphic designer you need to become conscious of those symbols.