A good way to get some insight into making your own designs is to look at what other people have done before. Take a look at this pattern called Anemone which is on the cover of the Dover publication Tatting Doilies and Edgings edited by Rita Weiss.
This doily obviously has some good negative space, but that's only one thing that makes this an interesting doily. What are the other features being used here to create this design? How do you think the designer was able to create a doily the perfect size to fit the surrounding motifs?