I've only been using Photoshop for about 3-4 months so this is the first tutorial I've ever made so enjoy. :P

Blood

1) Start out by creating a new white document. Mine is 400x400.

2) Go to Filter >> Render >> Clouds

3)Then, go to Filter >> Brush Strokes >> Ink Outlines with these settings :
Stroke Length: 50
Dark Intensity: 50
Light Intensity: 5

4) Duplicate your layer and set the layer's blending mode to 'Lighten'.

5) Go to Edit >> Transform >> Rotate 180°.

6) With still the duplicated layer still selected, open up the Hue/Satuaration Box with there settings :

Hue: 0
Saturation: 25
Lightness: 0

7) Go back to your original layer and open up the Hue/Saturation Box again, with these settings :

Hue: 0
Saturation: 100
Lightness: 0

8) Merge both layers.

9) Go to Filter >> Blur >> Guassian Blur with these settings :

Radius : 0.3 pixels