Hi !
Best way to promote your web design business is to offer something special. There are many web designers selling same stuff.
Create something that's not easy to find anywhere. like custom theme or application. Building starter website or display websites won't be enough. There are many web builders out there, make it easy to build websites.
Someone created over 180 types of websites to show her skills and eventually she was hired by many to build their websites.
Good luck.