Clean and simple is one of the most challenging styles of cardmaking for me. I was never a fan of white colored background, because it's really hard to make the card not look unfinished with a lot of plain white. I am also not a clean person :D so making a motif, that would add the desired interest, but still would go with the simple style is nothing easy for me. So I would say, clean and simple is not a style for everyone and you have to get to certain level of experience if you want to make it work.
The first card I tried to make in this style is a fall themed card for any occasion with a "For You" sentiment. I made the sentiment stamp and the leaves in Photoshop and then printed them and cut around. The background stripe is made with script stamp and distress inks.