Keep it short and recognisable
Your business name is usually the best starting point. If that is unavailable, a location or clear service word can work well. Avoid strings of keywords, awkward hyphens and unusual spellings.
Choose an appropriate ending
.co.uk is familiar and credible for a UK-focused business. .com is also a strong option, particularly if you may work internationally. Other endings can work, but clarity matters more than novelty.
Keep ownership in your name
Your domain is a business asset. Register it through an account you control, keep the contact details current and enable automatic renewal. A web provider can help configure it without owning it for you.