Rotating Layers in Photoshop
When using photoshop brushes a handy technique is to create layers and add brush marks and then rotate or flip the photoshop layers. This can offer several more variations to each photoshop brush.
Create a new document or open an image that you want to use, now we need to create a new layer from the layers palate as shown on the left. Select the Airbrush Tool from the tools palate, and spray a colour over the new layer. for this tutorial I am using the tank drawings from the photoshop brushes download section.
Now you have added some colour to the new layer, go to the top menu in Photoshop then go to 'Edit > Transform this gives you a large selection of options as shown on the left, most are pretty straight forward but I would recommend trying them all out to see what each one does.
Below is the Duplicated Photoshop Layer flipped horizontally duplicated and rotated 90° then flipped horizontally.