A lot of people have a hard time figuring out what keywords to optimize their sites for. This problem arises mostly with people new to building and marketing websites, or people new to SEO (search engine optimization).
One common mistake that people make is they make their keyword the same as their domain name and their site is optimized for that. This is not smart at all.
What you need to ask yourself when figuring out what keywords to use is, "What will people be searching for?". A lot of people who have domain.com will promote their site as "domain.com" or "Domain".
First thing's first, remove the .com. Next thing to do is go to Google Trends and see what people are searching for. This is completely optional but it helps in getting traffic to your site. When you go to Google Trends, find the search term that best fits your site and optimize for that term or a similar term.
If you have a site on flowers and you see the term "flower site" in Google Trends, optimize for it.