Three of anything that is, three colours, three images, three stamps, three words, the number three.... it's up to you, but don't forget the white space, a simple design and just one layer!
I have matted the card on black for the scan - my three is three pink flowers
White card from stock
Image - Stamp It - Antique Flower Trio
Ink - SU Basic Black and Regal Rose, Marvy Marker Olive
Sentiment DC195 - no brand