Choose your audience

The first thing to do when picking a right domain is to pick your audience.Your audience can be classified based on your clients, customers,geographic locations and so on. TLDs or top level domains like .com .net .org are fine even if you don't have a global presence. But if your strictly targetting a particular country say the UK or Japan, then a .co.uk or co.jp might do the job.My advice would be to stick to a dot com as its already captured the minds of the people.

Make it Crisp and Easy to remember

Short domain names are often a big hit.This is because of the normal human tendency to forget long words. Restrict your domain name to one or two words maximum and let it be easy to remember.

Strong Keywords

Use a popular keyword in your industry if possible in the domain name

Offline Business

If the domain name is going to be used to promote your offline business then, choose a name very close to your business

Dont Deviate from your business

Just for the sake of the domain not change your business image.This means that dont mislead your audience by choosing a wrong domain name.

Numbers

There has always been a debate regarding the use of numbers in the domain name.Numbers like 0 and 1 are confused with characters like O and L.Avoid numbers in domains.

Avoid Hyphens

Hyphens are known to be popular SEO tactic. But still,getting people to remember the "-" is a impossible task. Stay away from hyphens.

Get a proper registrar for the domain.

Most often people complain of domain hijacking. You can avoid this by using reputed services like GoDaddy or ENOM for the registration.

Register for a long period Its a good practise to register a domain name for atleast 5 years or 10 years although your business might not be centered around it.This helps your avoid bad experiences like some one lese using the domain you advertised.

Last but not the least

Think twice before getting a domain name.and stick to only one domain for a business.