1.    Short – it should register to the mind of the people and should be easy to type in the browser.
2.    Dot What? – choose the extension name that will be appropriate for your business type. .com is the
oldest and most popular extension name.
3.    Avoid Trademark Names – this may lead you to copyright violations.
4.    Register Domain now – do this now while you the opportunity.
5.    One may not be enough – having many domains isn’t bad; it may bring more of your popularity.
6.    Characters Type - just use letters, and stay on lowercase, though domain name is not case sensitive
7.    Ask around – you should be getting opinions from others so that you can have their insights.
8.    Don’t shell out on large amounts – you can use recycled domain either.

SEO Benefits

There are many cases when the major search engines will provide higher search engine rankings for web pages that have country-specific TLDs. For example, if an internet user from Canada is searching for software consulting services in that specific country, the site at mysoftware.ca may rank higher than another website with a .com extension selling the same product. This type of domain can also help increase your visibility through directories commonly referenced by local web surfers. Directories make a great way to enhance search engine rankings and build qualities links that lead to more traffic to your website.

Source: Web Hosting Geeks