There are a few great plugins you can install which are free - a lot of the self proclaimed "seo experts" will do little more than install these on your blog and then charge you a few hundred or thousand dollars. Here goes..
1. Platinum SEO - self explainatory plugin - which is already pre-configured to work well right across your blog, improving seo with every post.
2. Broken link checker - search bots hate broken links and this plugin will keep you infomed of any pages with broken links.
3. SexyBookmarks - dont worry, nothing too risky - but a very effective social bookmarking plugin which you can set to your own style.
4. Google xml sitemaps - essential plugin - again just install.
5. seo Smart Links - this one is the best of all - it is configurable to let you link both internally and externally on posts added to your site each time a keyword is used - for example if your blog is about fishing and you have a page about FRESH WATER FISHING you can set the plugin up so that any time you mention FRESH WATER FISHING it will link back to that page internally - this is again essential for good seo.
Hope this helps but if you need any more on this just let me know...