On the whole it's best to choose a Domain Name that matches your company name. If someone already knows your business name, they are likely to use that when trying to locate your website.
E.g. If your business is called ABC Crafts Wholesale then abccraftswholesale.com would be a good choice.

If your chosen name is not available, why not try a slight variation of the name.
E.g. if billbrowncrapbooking.com is taken see if
bill-brownscrapbooking.com is available.

Try not to pick a domain name that is extremely long and therefore difficult to remember, or time consuming to enter in a web browser.

Try sticking with a .com extension if possible. .net is usually associated with network services and .org with non-profit groups. .ca (canadian) is a good alternative to .com, but be pre-pared to pay slightly more for registration.

When you purchase a Domain Name it is not yours tor keep. In reality you are just renting it for a period of time. Usually in increments of 1 - 4 years. If you do not renew it before it expires, it then becomes available to anybody else to purchase and use.

The majority of Domain Name registration companies give discounts if you register the domain name for more than the usual one year time period.