The headline is perhaps the most important piece of your landing page. It is the first thing a potential customer sees. It is also the first marketing message your deliver. The goal of the headline capture the visitors attention and compel them to read the rest of your sales copy.

The best way to capture a visitors attention is to demonstrate your landing page is relevant to the search term. If a visitor believes the landing page will satisfy the reason for the search, they are more likely to remain on the page. If you can display the visitors search term in or around your headline, that will convince the customer that you landing page is what they are looking for.

Assuming you only one keyword in your ad group, or at least on a few terms centered around a single keyword, you can put that single keyword on your landing page. If you can incorporate that kewyord into your sales copy, the more likely the visitor will stay.

Adwords Dynamic Keyword Insertion provides a more flexible means of determining the visitors search term. First, you add a querystring parameter to your destination url. The parameter could be named something like "SearchTerm". Then, use Dynamic Keyword Insertion to to supply the value of the parameter.

Dynamic Keyword Insertion will replace the Adwords tokens with the search term the user searched for. This means that the destination url will contain the exact search term. This is more targeted than putting your keyword in the landing page.

Your landing page must be able to generate dynamic content. You want your landing page to check for the SearchTerm parameter in the querystring. If found, display it as your headline or part of it.

This technique will make your landing page more relevant for your users. You should get an increase in conversions.