Registering a domain takes about two minutes. The decisions worth pausing on happen before that (the name itself and the extension) because neither can be changed afterwards. Moving a name to a different extension is a new registration, not a setting.
Check availability
Search for the name on the domain registration page. If it is taken, you will be offered alternatives on other extensions.
Resist the urge to fix an unavailable name with a hyphen or a deliberate misspelling. Both fail the telephone test, "is that with a dash?" is a question you answer for years, and a clean name on a different extension is almost always the better outcome.
Check how the name reads run together, which is how it appears in a URL. Word pairs occasionally produce an unfortunate third word, and it is better to notice now.
Choosing the extension
Two things genuinely differ between extensions, and both are worth checking before you commit.
The renewal price. Some extensions register cheaply and renew at several times that. The renewal figure is what you pay every year afterwards.
Eligibility rules. Many country extensions require a local presence or a registered company. These are registry policies and no registrar can waive them.
What does not differ is search ranking. The extension has no effect on it, despite persistent advice to the contrary. Understanding domain extensions goes over the rest of the decision.
Ordering
Add the domain and choose a term. Multi-year registration removes the annual renewal failure point, and registries generally allow up to ten years.
Two options appear at checkout.
WHOIS privacy. Replaces your name, address and phone number in the public record with a proxy service. Worth having if the domain is registered to you personally, without it, your home address is publicly queryable. Some extensions do not permit it at all. WHOIS privacy protection goes into the decision.
Auto-renewal. Leave it on. More domains are lost to a forgotten renewal than to anything else.
Contact details
These become the registration record, and accuracy is a registry requirement: deliberately false details can result in suspension.
Use an email address you actually read, and not one on the domain you are registering. Verification messages, renewal warnings and transfer approvals all go there. An address on the domain itself means that when the domain has a problem, the warning about it disappears too.
Most extensions send a verification email after registration. Failing to click it can suspend the domain within a couple of weeks, so if it has not arrived within a day, check spam.
After registration
Point it at your hosting. Set the nameservers to the two in your hosting welcome email. See updating your nameservers. Propagation takes up to 24 to 48 hours.
If you registered the domain with the same order as hosting, this is usually done for you. Confirm rather than assume:
dig NS yourdomain.com
Confirm the registrar lock is on. It normally is by default, and it is the main protection against a domain being transferred away without your knowledge. There is more in domain locking.
Note the expiry date somewhere outside the registrar account.
What you cannot do afterwards
Change the name. Change the extension. Transfer it to another registrar for 60 days.
Everything else (contact details, privacy, nameservers, auto-renewal, the lock) is adjustable at any time, so those are not decisions to agonise over now.
Trademarks
Registering a domain grants no right to use a name someone else holds as a trademark in your field. Availability at a registrar says nothing about that.
A quick trademark search before committing a business name to a domain is worth the few minutes, particularly if you intend to build a brand on it. Discovering the conflict after two years of marketing is considerably more expensive.
Before registering anything, How to Choose a Good Domain Name explains the test that catches most bad names.
Confirm what you actually registered
The record is created within minutes and is worth reading once rather than assuming the form was filled in correctly.
whois example.com | grep -iE 'registrant|admin email|expir|status|registrar:' dig example.com NS +short
Three fields matter immediately. The contact address, because verification and renewal notices go there. The expiry, so you know when it renews. And the status lines, since a newly registered domain carries a hold until the address is confirmed.
An unverified domain is suspended rather than merely flagged, and the suspension arrives days later when everybody has forgotten the confirmation message.
Point it somewhere before you need it
A registered domain that resolves to nothing is a name doing no work, and the first thing anybody who hears about it will do is type it.
dig example.com A +short curl -sI http://example.com/ | head -1
A single page saying what the name is for costs minutes and is considerably better than an error or a provider's default page carrying somebody else's branding.
It also lets you confirm the delegation is working, which is a separate question from the registration having succeeded and one that is easier to answer now than during a launch.
Set the renewal up on the day you register
The renewal is a year away, which is exactly why it is arranged now or not at all.
Enable automatic renewal, confirm the payment method will still be valid, and set the contact address to something that does not live on the domain being renewed.
whois example.com | grep -iE 'expir'
That last point is the circular failure worth closing immediately. A renewal notice sent to an address at the domain is undeliverable once the domain lapses, and the notice about the lapse is the one you needed. Domain auto-renewal covers the rest.