WordPress itself is very search engine friendly and blog or website whatever you make with it is indexed well without any problem. The inbuilt features like tags, categories and archives also add to the search engine friendliness. Adding few more plugins to the wordpress makes it really well optimized with least effort and time. Here are some of those must have wordpress SEO plugins:
1. All in One SEO Pack: This one plugin does several jobs, first it will create meta description, keywords and canonical for you which is the most basic requirement for optimization. Then you can use it for generating XML sitemap and submitting it to Google, it does both the work with few clicks of button.
2. Authorsure: ever wondered how people get their profile picture besides their website link in search results? This plugin will make that possible for your blog/website too. This is a new technique called structured data which Google recognizes if it finds it in your page and display your Google plus profile besides the search result from your website. This is not just to show off but helps in several ways, first it makes your website link stand out from others and therefore get more clicks. By adding your profile picture you are also adding acknowledgement to your website result in search engine as your profile is also linked now. Google will give priority to such websites and it climbs up in search results.
3. Social plugin: Actually this is not a name of any plugin and I purposely did not name any particular social plugin here. Important thing is that you do add major social networking profile links to your site/blog. Either you add manually by adding buttons in sidebar or use some plugin. Choose any good social plugin which suits your WordPress theme. Adding link to your social profiles page is good for SEO purpose and also let your visitors visit your social page.