A landing page is the page someone arrives at from an advertisement or a campaign.
Why not the home page
A home page describes everything the business does, which means it answers nobody's specific question. The visitor searched for one thing and has to find it.
A landing page matches what was searched for and asks for one action.
What it contains
The offer stated in the same words the advertisement used, so it is obviously the right place.
What the business does and where it serves, immediately, without scrolling.
Proof: reviews, licences, insurance, years in trade — see customer reviews.
One call to action, repeated. Call, book, or request a quote — not all three competing.
A phone number that dials on a phone, since most of this traffic is on one.
What lowers conversion
More than one thing being asked for.
Long forms. Every extra field costs responses, and most fields are not needed before a conversation.
Anything that looks like a cost the visitor did not expect, revealed late.
No indication of response time. Urgent work turns on who answers first — see improving close rate.
Conversion rate
Enquiries divided by visitors. It is the multiplier on everything paid for upstream: doubling it halves cost per lead without changing the advertising at all.
That makes it usually the cheapest thing to improve in paid marketing, and the least often looked at.
One per campaign
A page per service or per area lets the message match the search. It is more work and it is the difference between advertising that pays and advertising that nearly pays.