You should focus on the best root keyword for the main keyword, and "bring in" the related long tials.. Use the root keyword in the title, desc, h1 tag, in the opening and summary paragraphs. Spread use of the root keyword across the page, so it is evenly distributed and not bunched at the beginning or end only. Use a mention in the opening paragraph to bring in the longtails, and create a h2 heading for each one. Put content under this heading about the longtail, and keep most other keywords out,except maybe the root.
Your goal here is to keep the information about the long tail keyword in close proximity of its h2 tag, and not under any other h2 tags.. Use h3 tags if possible to further develop this long tail (or to brig in longer tails of this one), but keep all other long tails out of this one's H2 umbrella.
When you mention the long tail in the opening paragraph, you signal that it is important to the page. When you add it to an H2 tag, you are giving more weight to the phrase, because of the algo. This will almost always bring in a long tail on a page, if the long tail is related..
You target the root keyword because some people in your area will search for it. Because SERPS blend their results between local and global results, when someone searches for the root keyword in your area, you will pop up in the serps even if they did not search by city name. Keep in mind that they have now entered your site not on a long tail, but a root keyword. Now, if they stay on our site it is an indicator that they found value in your page, for the root keyword. When this happens over time, the algo will adjust your ranking up for this root keyword upward, until it matches the competition, or beats them. This is slow ranking, but when it happens, the strength of the national ranking really cements the local ranking in place, making it almost 10 ft tall and bulletproof.