Search Engine Optimization and Marketing without copywriting is pointless. There I said it.
Writing effective copy is a combination of information, details of your products or services and a little something special called emotion. When you evoke an excitement about your company and a call to your cause it results in traffic, buzz and sales.
The importance of copywriting for SEO is a very thin line that borders between writing for search engine spiders and human visitors. With advances in search engine indexes focusing more on content than Meta code, it is vital to keep the search algorithms in mind. At the same time your emphasis should be on writing for people, since search engine spiders have no money to spend (and they certainly won't tell all their friends and colleagues about you). Incorporating search terms into your copy and applying strong tags will be sure to make everyone happy. After your copy is inserted clean it up with proper validation. This will make search spiders happy as well as your visitors.
Keeping your copy relevant and organized is another crucial step to maximizing your online potential. Stay on topic, retain a common vibe throughout the site and stay coherent. Its easy to get off topic when you are passionate about something, but save it for another paragraph or page. It makes your information easier to index and you avoid sounding like a crazy person.
Copy needs to have proper grammar, spelling and punctuation. Commas are no excuse to chop up what I can clearly see is a run on sentence. Capitalize where appropriate and keep in mind that not everyone knows abbreviations and industry specific terms. Feel free to use spell check (it's in every piece of text editing software and even the firefox browser). Also take note of context; there, their, they're all mean something different.
Oh and did I mention punctuation and spell-check? Good.