A good domain name is memorable. www.yourbrand.co.uk.  If your business name is long, try shortening it.  We opted for www.monster-it.co.uk instead of www.monsteritservicesltd.co.uk.

A professional domain name is good for branding.  When you're looking for a credible company, you wouldn't necessarily trust a business with a Hotmail account over a professional domain name.  Once you own your domain you can have it for life.  Just like your mobile phone number, you can take it with you wherever you go.

Make it relevant to your business.  If your business is an accountancy firm which happens to be called after the family name, for example Goldsmiths, you may wish to buy a more relevant domain name so as you aren't getting search results for people looking for jewellery.