For one thing, SEO and PageRank are not the end-all-be-all of web site design. Use keywords and links placed in relevant locations to guide people to your helpful information, not your ads.
Those are good things to improve PageRank. Keywords do not improve PageRank but instead help search engines know what your site is about and what search terms are going to be relevant. Again it all ties into how your site is helping your visitors. High-quality sites are always best; focus on that and you will find it will help you a lot.