The longer your domain name is, the harder it is for people to remember it and the more chance you have of someone misspelling one of the words. Most good single word domain names are long gone, but you can still avoid long domain names by getting a little creative. If you have a single word you really like that is not available, try adding an adjective or verb in front of it and seeing if those variations are available. Think of your domain name as part of your brand, and make sure it matches how you want people to think of you.
When looking up a bare name in DNS, the network stack will add the search domains to it to form fully qualified domain names, and look up those as well. For example, if the domain search list contains "wikipedia.org", typing "en" in the browser will direct the user to "en.wikipedia.org". Some ISPs add their own search domains via DHCP settings, similar to how they add DNS servers and other networking information; if this is undesired, the user can change this setting to ".local".
Many online shops have the number 24 in them, to signify 24 hours a day – you may also be able to integrate numbers into your domain in a meaningful way to make them unique. Be careful though, because many cultures attach a lot of significance to certain numbers. Make sure that your number doesn't represent bad luck or other negative things in the country you're operating in.