The Cretan stitch is an easy relaxing stitch which lends itself to all sorts of simple and complex variations. 
Stitches can be close together (like a leaf on a tree), or wide open with the stitches evenly spaced apart or stitched at varying angles. The stitches can be worked up and down, left and right, or slanted.
Use different size threads, For example, use a heavier thread on the bottom and then stitch on top with a finer thread.
Here is another sample by Margaret Preece stitched on a cotton background. She has created a whole picture using just Cretan Stitch in several variations and threads including metallic ones. Some are shiny; others are flat and ribbon-like; some are fine cords. She has used in addition to plain Cretan stitch, open Cretan, Scottish Cretan, closed Cretan and laced Cretan.