A domain name is the one decision on this list you cannot cheaply revisit. Changing it later means redirects, lost links, reprinted materials and explaining the change to everyone who knew the old one.
Which is an argument for spending an hour on it, not a week.
Short, sayable, spellable
The practical test: read it aloud to someone and have them type it without asking anything.
That single test catches most problems. Names that need spelling out, words with two accepted spellings, letters that sound alike, and anything where a hyphen might or might not be there.
Shorter is better because it is typed more accurately, not because of any ranking effect. Under fifteen characters is a reasonable target and not a rule.
What to avoid
Hyphens. People forget them, and a competitor holding the unhyphenated version receives your traffic. If the version without hyphens is taken, that is information about whether this name is available instead of a problem to work around.
Numbers. Is it "4" or "four"? Both, and you now need both.
Doubled letters at word joins. The classic problem where two words collide into something that reads as one long unintended word.
Deliberate misspellings. Memorable in a pitch, mistyped forever afterwards.
Choosing the extension
.com remains the default assumption. People type it without thinking, and if you hold something else, some of your traffic goes to whoever holds the .com.
A country extension is the right choice when your business is local. It signals where you are, and customers in that country trust it.
Newer extensions can work well when the name reads as a phrase. They are not penalised in search, and the honest caveat is that some people still type .com out of habit whatever you tell them. Understanding domain extensions walks through the trade in more detail.
Check the name, not just the domain
The step that prevents an expensive mistake.
Search for the name and see who is already using it. Check trademark registers in the countries you operate in. Check whether the social handles exist.
A domain being available does not mean the name is. Registering a domain that infringes an existing mark can end with you losing it and rebuilding your identity, and the cost of checking first is an hour.
Do not buy every variation
Registrars will happily sell you twelve extensions and every misspelling.
For most businesses two or three is enough: your main name, the country extension if relevant, and the obvious singular or plural. Point the extras at the main one with a redirect. A parked domain alias in cPanel does this without duplicating the site. Addon domains and duplicate content explains why an alias in place of a copy.
Defensive registrations only make sense once a name is worth defending, and by then you will know.
Keywords do not do what people think
An exact-match domain is not a ranking strategy. Search engines rank content and links; the name in the domain contributes very little.
What a keyword domain does give you is a name that describes the business, which helps a human decide whether to click. That is a real benefit and a different one.
The cost is that it locks you in. A name describing one product is awkward when you sell three, and a name naming a city is awkward when you expand: that flexibility is usually worth more than the descriptive value.
Room to grow
Pick a name that still fits in five years.
Businesses change what they sell and where they sell it. A brandable name that means nothing on its own accommodates that; a descriptive one does not, and renaming later costs everything this article opened with.
Register it properly
Once you have chosen, four things at registration:
Correct registrant details, in your name or the company's. The registrant is who legally holds the domain. A domain registered in a developer's name is theirs.
A contact address you read, not on this domain.
Auto-renewal on, with a valid card. For that, see What Happens When a Domain Expires.
Privacy protection, unless your registration details need to be public. For what it hides, see WHOIS privacy.
Then enable the registrar lock, which stops the domain being transferred away without your involvement.
A quick shortlist test
Say it on the phone. Have someone type it. Search it. Check the trademark. Check whether the .com is held by someone doing something similar.
Then choose. Domain names are decided badly by committees and reasonably by one person applying those five checks in an afternoon.
If the name you want is already taken, buying it second-hand means inheriting whatever it was used for. How to Buy an Aftermarket or Expired Domain Safely goes into checking first.
A name registered for later still needs three records, or anyone can send mail claiming to be from it. How to Park or Hold a Domain Before You Use It goes into it.
Say it out loud to somebody else
The test that catches most bad names costs nothing and almost nobody runs it.
Say the name to a person who has not seen it written and ask them to type it. If they hesitate, ask which spelling, or produce something different, the name will cost you traffic every time it is spoken rather than clicked.
The common failures are predictable: a word with two accepted spellings, a number that could be a digit or a word, a doubled letter across a join, and anything relying on a hyphen. Each is fine on a business card and expensive on the radio.
Do this before checking availability. A name that fails this test is not worth registering however available it is.
Check it is not already something else
A name that is free as a domain may be thoroughly occupied everywhere that matters.
whois example.com | head -5 dig example.com A +short
Search the name as a phrase and see what already ranks. Competing against an established meaning is a long project, and discovering it after launch is the expensive order.
Check the social handles at the same time, and check for an unfortunate reading when the words are joined without spaces. That last one is a genuine category of mistake, it is permanent once printed, and it takes ten seconds to avoid.