Filter Render Options for Clouds

You can control the density by using a new document, and setting image size to suit.  Then Free Transforming to the required size in the master document.  If you canvas is 2000 pixels square, and you create a 4000 pixel square document, Render > Clouds will have double the density.

I think the Ctrl Alt F to increase the contrast trick changed a couple of versions back.  Probably with CC2017 with the introduction of the wonderful new Search tool.  So you might find you need a different shortcut if using CS6 for instance.

The name Render > Clouds is a bit of a misnomer as the effect isn't remotely like clouds.  It's mostly a tool to randomise tonal values across an image or texture.  As in the variation of light and dark in this illustrated denim.  You can Render Clouds directly into an Adjustment Layer's mask for instance.

If you are chasing a particular effect, then if you give some details, we might be able to help.  If you want to create actual clouds, for instance, then there are enough cloud brushes out the to achieve a unique random cloud texture.  My tip with using cloud brushes is to add a drop shadow.  Also layer the clouds and make them smaller and feinter into the distance, and in some cases use Create Layer to separate the drop shadow layer style to a separate layer, and clip it to the cloud layer beneath it. (high Clouds throw shadows onto lower clouds)

In addition one can press the Alt/Option key when going to Filter>Render Clouds or Difference Clouds to get more contrast in the effect.

No there is very little control.

You can change the foreground and background colour prior to rendering and you can use the layer opacity /blending controls etc after render.

Dave