You should start SEO (Search Engine Optimization) before website development. This is contradictory to conventional marketers’ way of building a beautiful website; and then #SEO.
The rationale behind lies more on the onsite optimization elements such as website content structure, website design and layout, content writing and programming that is related to your keywords.
Some non-SEO friendly elements in the website may not be reverted once the website has been built. The classic example includes but not limited to one-page layout, websites for separate devices, content structure not in line with SEO keywords objectives, etc.
For more information, please visit:
http://www.digital-communication.com.hk/SEO-Search-Engine-Optimization.htm