First of all you'll need at least two calligraphy pens in toning colours. I've used a light and a dark one from the Heart pouch set.
What I then did was touch the side of the lightest pen with the dark pen.
This will allow you to write in two colours.
I kept the darker edge of the pen still and moved the light side in a rough quarter turn and got a petal. I then moved the paper a bit and repeated the above. I did this until I got about 5 petals. Just remember to move the paper round every time you want a new petal.