Selecting the domain name for your business is crucial. It’s part of your brand and plays an 
important role in your internet marketing.
If you’re in a particular niche, you’ll want to choose a domain that includes a KEYWORD that users search for to find your site. So, for the guy who wants to teach people how to be more social he’d choose something like howtobesocial.com.
You’ll find a lot of the domain names you want are probably sold already, so you’ll have to be quite savvy to find one you want.
Which suffix should I choose?
The top-level domain (TLD) is whether you’re going to be called a .com, .co.uk, .net or .org. If you are UK focused choose .co.uk, world focused try and get the .com. You only want to use .org if you are a not-for-profit organisation.
What if my domain has already been taken?
If the domain you wanted really has gone try re-wording the keywords and put them in a different order or try turning nouns into verbs. Also, you can check whether the existing name owners are actually using it for anything (use Whois.net for that). You can contact them and see if they want to sell it for a reasonable price.
Try to buy as many combinations of your keywords as possible, as well as covering the main TLD’s. Domain names are cheap, so don’t be too cheap and regret it later!
I use Fasthosts or 123reg to buy my domains.