Options for domain names can be little tricky and finding a suitable choice is a very important matter. The name you choose will be used by search engines like Google to make sure your site accessible to their viewers.
There are several factors which go into the decision which should be considered. The foremost is that your choice should be direct and as meaningful as possible. If you are creating a website for a store which sells boots, you would want to choose a name which incorporates “boots” or a relative word in the domain path.
The next suggestion I would make is to keep your domain name as succinct as possible. When a domain is long, there is more room for error and the chance that someone will mistype. It can become an issue when the error leads your user to someone else’s site.
With the same token, there are a great many extensions available currently such as .com, .co, .net, .org, .us and the like. They certainly bring much to the choices but you don’t want your “boots.co” request going to “boots.com” if you both sell boots.