I've had SEO consultants swear that you should still fill out the meta keywords tag because some search engine in a galaxy far, far away is apparently still giving it some clout. I say leave it blank. The search engines that matter won't give you anything positive out of it, and you never want to find yourself in a position where you're actually getting dinged for having that field stuffed with too many keywords, or having the same keywords duplicated across every page.

I also agree with Donna that it's making it easier for your competitors to see what you're targeting.

If you ever have a client who demands to know why you're not including meta keywords, you can show them this blog post directly from Google that pretty definitively states that they have no ranking value: http://googlewebmastercentral.blogspot.com/2009/09/google-does-not-use-keywords-meta-tag.html

I would optimize the pages that you want to drive traffic to for keywords that are naturally relevant to each page. Never stuff a page with keywords (use your gut to determine the right amount) and always write copy so that it is completely readable and not awkward for your visitors. I would also avoid creating multiple pages just for the sake of targeting similar keywords with no other purpose (e.g. you have a page that targets "red apple" and a page that targets "red apples"). I've seen sites get smacked by Google Panda for doing this.

Sites with poorly-written SEO copy seem spammy and will be an instant turn off to whoever's showed up at your virtual doorstep.

Pages such as Contact Us and About Us don't really need optimization per se. However, all pages should at least contain unique and relevant h1s, meta titles and descriptions. Also, always avoid duplicating text between pages. This helps your website be more search engine friendly. I find that the Screaming Frog SEO Spider and Google's Webmaster Tools HTML Suggestions are great for diagnosing which pages on your site need these unique elements.