Google Page Rank should just be one of many signs of a healthy blog/site, but one way to ensure it doesn't drop and possibly even improves over time is to keep the following rules in mind for any content you create:
1) Always provide useful, original, and natural copy on your pages.
2) Keep your "do-follow" links to external sites to an absolute minimum.
3) Use "do-follows" to links within your own site when it makes sense.
4) Keep affiliate links "no-follow"
5) Clean up your posts/pages periodically to eliminate links that are broken, expired, or do not follow Google's preferences.

These are just the basics. There may be other things that are keeping your pagerank below your preferred goal. We can chat more if you're interested! Good luck!