Creating Lace Designs in Photoshop
I actually first discovered the basis of this process through a tutorial on the Shashinya no Tesaki site. Unfortunately, it's no longer active, but you can find the original tutorial on the internet archive. If you want to see this process in action, a video tutorial is available on YouTube.
This is essentially the process I used while making the Doily Disaster brush set.
Start up Photoshop, and create a square file.
I'd recommend 500px x 500px at minimum. Square files make this a little easier.
Open up the Brush panel...
Once open, choose a basic round brush. Adjust the settings so that the spacing is anywhere between 70% and 90%.
You may also want to turn off pressure sensitivity.
Create a new layer and draw your design.
You will also want to make sure your design is aligned horizontally.
You can do this using the "Move Tool" in Photoshop. You should see the following toolbar to complete this:
Once your image is centered, duplicate the layer.
Right click on the layer in question and select "Duplicate Layer..."
Use the "Free Transform" option to rotate your duplicated layer by 180°.
"Free Transform" can be invoked by selecting the entire image (ctrl+A [Win]; ⌘+A [Mac]) and right clicking.
You'll then be able to right click again and specify the angle you'd like to rotate to.
Merge your layers together, and then duplicate again. Rotate by 90° to get four copies of your original design.
You should have something like what's shown below.
Merge the layers again.
Afterward, duplicate the newly merged layer.
Once more, rotate one of the layers by 45°.
At this point, you can merge it all together, and fill the design if you want.
Once you're comfortable with the basics, you might want to try changing things up!
Experiment with different angles (eg: 30°, 72° and so on and so forth...)