After viewing umpteen pieces of art and designs for greeting cards, I decided to write about design and layout. I have over 20 years experience in the advertising world as an art director, so I have a lot of experience in this field. I can't possibly give a course, or solve everyone's design woes, but there are just a few basic concepts that may help. First off, make sure your art or photograph is professional looking. I'm not talking perfection here, but at least make an attempt at creativity and make sure your jpeg/png is of the highest quality and standards that meet the criteria to the site you're uploading to.
I equate designing an ad/card/art/photograph to dressing. The more you load onto your outfit, the worse you'll look. Imagine you're in a polka dot dress; you add a bright colorful flowered shawl, huge garish earrings and work your way down to adorning your wrists with loud bangles and ending with patterned stockings and obnoxious shoes. No one is sure where to look, and nothing stands out. It's all just a visual assault. Yes, there are those that will say you look great, and I see those compliments all the time attached to the worst art out there.
Now you've changed.... and you're now wearing a beautiful dress, flattering to your figure with the most beautiful necklace to set it off. The dress is not patterned and the necklace enhances your gorgeous hair and face. You walk into a room where you are now a breath of fresh air and not a visual assault.
Keep it simple. Pick something to be the showpiece. Don't be afraid of a little breathing room, a place for the eye to rest. Don't divide your page in half. Don't make things equal in size. Something needs to take center stage. The visual should be clear and convey the message. It should be pleasing to the eye.
Text should be readable. No more than 3 different styles of type. Learn about kerning and leading.
It's the small nuances that make or break how the text looks. It should hang together, not look like it's floating apart. It should work with the art, not against it. And make sure your card visual makes sense to what the card is about. If it feels forced, it is! I've come to learn that it really isn't about drawing perfectly, it's about CONCEPT/IDEAS. It's that way in music, art, writing, etc. Concept first, execution next.
My first love is drawing, but I ended up as an art director because I didn't want to be a starving fine artist. But I have to say that the experience I've garnered has been invaluable in understanding many creative businesses and how it takes more than just being artistic to sell. And that's really the bottom line; you're selling your product and you have to be as attractive as possible to the consumer.