Nodes: Flood Fill, Flood Fill to Random Grayscale, & a Blend

This is an easy way to create variations from patterns. To start we are going to need a tileable pattern with its edges detected & add a few nodes. "Flood Fill" to obtain pattern information & "Flood Fill to Random Grayscale" to generate a variation of value.
You can adjust the node settings to your preference. Next, take the output of the Flood Fill Grayscale to the alpha channel of a Blend. Doing so you can mask in diffuse variations & use Blend's opacity to control the contrast.
Typically I like to add only a slight color variation. You can use this for something such as roof shingles (like I have above).

Nodes: Clouds 1, Blur, Slope Blur, Blend, & a Mask 

This is a continuation of my "Cracks With Shapes & Warp Node" tip. To add various chisel/chip effects to the cracks we created previously add these few nodes. Blur "Clouds 1" for a smoother look. Input the final version of your cracks in slot A & the blurred Clouds 1 into slot B of a Slope Blur node. Make sure the samples are at 32 & mode set at "Min".  You can slide the intensity to your liking - I like to stay between 1 & 3. You can use this for something such as tiles (like I have above).

Tip:  Tidy up your graph by docking your nodes with hotkey "D". 

Nodes: Blur, Tile Random, Level, Distance, Edge Detect, Directional Warp, Warp.

Using "Tile Random" with the shape set as a disc with level & scale variation applied you can create a base for cracks. Apply a "Blur" node to soften the edges. After, take the output from the "Blur" & use that as your input for the "Directional Warp" node. I like to use "Clouds 2" for the intensity input. To add more slopes to your cracks send it through a "Warp" node with "Perlin Noise Zoom" as the intensity input. You can always go to the "Tile Random" node to change up the scale, variation, & position for the base.

Tip: Click your Space Bar to pull up a search menu - this will save you time from scrolling in the library.