The basic procedure is this.
1. New file (I used 640 x 480)
2. Fill background layer with black
3. Create new layer
4. Fill with medium grey
5. Filter / pixelate / color halftone / radius 15 and other values all the same; I used 108
6. Select magic wand (contiguous NOT selected) and click on one of the black dots and press delete
When you use a different grey for your fill in step 4 you will get different results. Instead of using a regular fill you can also use a clouds or gradient fill so that the sizes of the dots will vary.
The first example was done with a dark grey, the one underneath with a light grey. Lighter tones will make the dots smaller. You can also experiment with a different angle or radius. Also try to experiment without doing step 6 and adding brushstrokes. That?s how the green texture was created.
You can use a dotted layer to create textures that have repetitive textures. Treat the dots as if they are just particles. Try to change their shape and suddenly you will have a totally different pattern.
Have fun!
Dots & textures 
Linear Mode
