Pick up the best performing keywords.just do not think about the high volume keywords but think of the keyword which are going to give you more business.It is also good to choose the keyword which have low volume of traffic with high conversion rate but dont choose a keyword with high volume of traffic but with low conversion rates.
Google has not used Meta Descriptions or Keywords in their algorithm for a while now. It's only good for the lesser Search Engines.
Yes keywords are an intricate part of SEO, but Google do not use the Meta tags for keywords anymore and have even said so in their Blog. They may use Meta descriptions for their snippets but afaik it has no direct affect on your ranking. Source: googlewebmastercentral.blogspot.com/2009/09/google-does-not-use-keywords-meta-tag.html
Bradrap is correct. Google does not use meta keywords or meta descriptions in their ranking algorithm... So I wouldn't lose a lot of sleep over picking keywords for your meta keywords. That being said... the <title> element of your page should indicate what keyword phrase(s) that page is targeting. All other optimizations to the page should be based on and reinforce your <title> element. . The <h1> and <h2>s on the page should target the same keyword phrase that appears in the <title> or slight variations of the phrase. . The content on the page should target the same keyword phrase that appears in the <title> or slight variations of the phrase. . The link text used to link to the page should target the same keyword phrase that appears in the <title> or slight variations of the phrase. . The meta description should contain ALL keywords that appears in the <title> since these will be the most likely keywords used to find the page in the SERPs. If all of the keywords in the user's search phrase appear in the meta description then Google will show the description as the snippet. If not then they will construct one using sentence fragments from the content of the page that contain all of the keywords. You want them to show your meta description so you can control what is shown and influence click-thru-rates. . The meta keywords should contain the same keywords that appear in the <title> or slight variations of the keywords (I only show the variations if they also appear on the page and limit to 5-10 keywords or keyword phrases at most).