I started by putting a small dot with my vanishing marker for the center of the snow flake. Then I just drew staight lines around it. The first snowflake bag I made (the pink one), I used a piece of paper for the center dot, to make the snowflake off center of the bag.
Once I had the snowflake sketched on the bag, I put a line of puffy paint and then painted it flat with my paint brush. Don't forget to put a some newspaper or wax paper inside the bag to avoid it from bleeding through.
I wasn't too concerned with the thickness of the lines, I wanted it to look a little worn.