This is one of my favorite techniques. The blend tool has lots of uses, but this one can be the most accurate and flexible for creating patterns.
Step 1: Create a Blend
First take a shape tool, any will work. It depends on what you would like your blend/pattern to be.
Draw a shape holding down the shift key to keep it proportional.
Then hold down shift and option then drag the shape to create a copy. Make sure there is enough space between your two shapes.
Go to the blend tool and double click it to bring up the blend options. Since we want individual shapes choose specified steps under spacing. Choose a number. For my example I chose 40. This will give us a total of 42, including the first two you created.
Now you use the blend tool by clicking both of your shapes. If you have done this correctly you should have an image like the one above.
Step 2: Create a Spine
Now we want to revolve our blend around a spine.
Create another shape with a spine. For my example I created a spiral.
Step 3: Replace the Spine
Select both the spine (larger shape) and your blended shapes. Go to object, blend, replace spine.
Step 4: Modifications
This isn't exactly what we wanted. So select your spine again, double click the blend tool and increase the number of steps.
Step 5: Final
I increased my steps from 40 to 70 and now the pattern looks much more even.