How to create a blurry background in Photoshop

Question

I want to create a background like this:

But gets like this (notice the spots and trails):

I tried with different color modes/bits per channel. It's always like that. What I'm doing wrong?

Answer 1

This is what I got:

1. Press X to set colors to black & white
2. Filter -> Render -> Clouds
3. Create a Levels adjustment layer, and move the slider to the right to increase contrast.
4. Select the Levels adjustment layer, and press CTRL+E to apply to the background layer
5. Filter -> Blur -> Gaussian Blur, and move it right until you reach the desired blurriness.

Hope it helps!