I'm going to show you how to make a wooden texture in Paint.NET.
Step 1: Pick your colors and make a cloud
So first your gonna wanna pick your colors. The ones used here are the orange and brown that are on top of each other in the paint pallet. Now, go to Effects>Render>Clouds and use default settings.
Step 2: Make some waves
Now go to Effects>Distort>Waves, and set them to Radius: 18176.97, X Effect: 7468.29, Y Effect: 389.37. You can mess with these settings to get a different grainy look.
Step 3: Soften, apply vignette, and your done!
So now your gonna wanna soften it. Effects>Photo>Soften Portrait and use default settings or other settings to get the colors you want. Once you've done that, apply a vignette at what ever settings you want. You can also go to Adjustments>Levels and move the bars up and down to change the color of the wood. This is perfect if you have the Shape 3D plugin installed so you can make a wooden ball.(See second picture)