Most SEO plugins have way too many bells and whistles for my simple needs, so I wrote a little snippet that's meant as a drop-in, DIY replacement for the big WordPress SEO plugins. If you want a lot of features and options, then try Yoast's awesome SEO plugin or the great All in One SEO; otherwise, if you just want something simple that works, check out Basic WP SEO — a simple slab of code that you add to your functions.php file and done.
In otherwords, match what you see when creating/editing a Post or Page in the WordPress visual editor to what you get when you actually publish it. It's easier than you might think! Basically you can declare a special CSS file that the visual editor will use to render itself while you are editing it. If the styles in that CSS file match the styles in your live theme's CSS file, you are straight up WYSIWYG (What You See Is What You Get).