Paid traffic should land on a page built for the single promise the advert made, not on the homepage, because a homepage is designed to serve everyone and therefore persuades nobody in particular. A visitor who clicked an advert about one thing arrives with a specific expectation and a short patience. A dedicated page that continues the advert's message converts that interest; a homepage makes the visitor search for it.
A homepage has too many jobs
The homepage introduces the company, routes visitors to services, reassures new arrivals and serves people who already know you. That breadth is what it is for. A visitor who clicked an advert for one service has to find that service among everything else, and the effort is more than many will spend, especially on a phone.
The advert has already done the work of choosing a topic. The page it leads to should take that choice seriously.
Match the page to the promise
The headline on the landing page should echo what the advert said, in nearly the same words, so the visitor knows they are in the right place within a second. Then give the one thing the advert implied: the offer, the explanation, the next step.
Remove what does not serve that purpose. Heavy navigation, links to unrelated services and secondary calls to action give a visitor reasons to leave a page you have just paid to bring them to.
One action, stated plainly
Decide what the visitor should do and make it unmistakable: enquire, book, call. Repeat it at the points where the visitor is likely to be ready, and make the route short. On a phone this often means a tappable number and a form with only the fields you cannot do without.
If the action requires explaining something first, explain it above the action, briefly, and let anyone who wants detail follow a link rather than forcing it on everyone.
Decide what search engines should do with it
A campaign page is rarely something you want in search results. If it duplicates content from a regular page, or exists only for a promotion, ask a search engine not to index it, and make sure its canonical address is deliberate. Decide this when the page is built; discovering a dozen near-copies in a coverage report two years later is a slow and tedious cleanup.
Conversely, if a landing page is useful enough to rank, treat it as a proper page of the site and give it unique, substantial content.
Measure each page against its own promise
Track what happens on each landing page separately from the site as a whole, because the comparison that matters is the page against the advert that feeds it. A page that fails might have a weak headline, a mismatch with the advert, or the wrong audience; keeping them separate lets you tell which.
Change one thing at a time. A landing page with several simultaneous changes tells you that something happened and nothing about why.
Speed matters more here than anywhere
Paid visitors are impatient and arrive mostly on phones. A landing page that takes several seconds to appear loses some of them before they have read a word, and you have paid for each of those. Keep the page light, avoid heavy scripts and large images above the fold, and test it on a mid-range phone over an ordinary connection rather than on the machine it was built on.