Follow the rules.
Firstly, create a new document. Control + N and set Width 500 & Height 500. click OK.
make sure the background is white
Go to filter > render > clouds. Follow the picture below.
And your image will be like..
Ok. We want to make it little bit blur. Go to filter > blur > Gaussian Blur. As shown as below. Set radius to 40,2
Colour the cloud with your favorite color. Go to image > adjustment > color balance or press Control + B. Then try to adjust a tone of color.
Your cloud will be colored. i choose a green color.
Pick any pattern or any image. Put into your project. Then make it black & white.
Image > Adjustment > Black and white or press Control+Alt+Shift+B.
Then apply the blend mode to soft light, opacity to 50. see picture below.