My ditto: Keep it simple, silly; never stop learning; and keep developing. Guide to a successfull Graphic Designer | -- Future reference because becoming a graphic designer is one of my goals. Not really related to photography, but it is a goal.
The golden ratio should not need any introduction to those who have studied math and design in school. Some designers apply these mathematical concepts to come up with more visually appealing works. This infographic from covers a few golden ratio facts:
Just did a card for a friend in 15 minutes on Vistaprint.com. Used to take weeks to design, meet, change, redraw, do layout, spec paper & color, deliver to printer, wait a week, pick up from printer. Now it's done in 3 days.