Before you get started on building your website, you need to focus on finding a great domain that will support you in the long run. At the very least, you should pick out something that's easy for people to type and remember, and really captures what your store is about. Try to find a domain name that includes your primary keyword, which should be the main type of product you sell.
Come up with a list of options based on available names and carefully consider each one. Does it have the potential to stand the test of time? Does it accurately convey a brand message? Is it niche-relevant and high quality? A bad domain name can hold your store back and seriously hurt your credibility over time.
One option that can be really effective is to use a domain that has some authority already established through previous use by another website. When a website is taken down, or the owners simply forget to renew its registration, you can snap up its domain
and build a new site that will benefit from Google's existing trust.
If you choose to try that route, look at metrics such as Trust Flow or Domain Rating
to get a good feel for how trusted a domain is. If it has some questionable backlinks, or if it seems like it may have been penalized by Google, don't risk it. It's better to start fresh with a decent domain than it is to try to rehabilitate a great domain that has been hit by penalties.