Optimize the right keywords
Optimizing your pages for the proper keywords is the smartest thing you can do. If you don't plan ahead or optimize for the right keywords your missing out on a ton of valuable high paying traffic.
The first thing I want you to do is go to goodkeywords.com and download the tool they have there. It will tell you the number of times a keyword or keyword combination has been searched for over a time period.
While it shows a "number", it's not quite accurate. Overture gets about 8 to 10 times less searches than google per month. It's a good indicator of how popular certain search terms hold up.
Now your just starting out, and your chances of getting ranked highly for a generic keyword is very slim. Instead of trying to optimize "keyword", try to optimize something a little narrower like, "Keyword Research".
Now you really shouldn't write for the engines. Write your content so it's readable, fresh, and above all navigatable.
If you write about your keywords, and use them in your content you will be just fine.