There are alot of useful Plugins that you can use for SEO on WordPress like for example Yoast. For beginners I recommend the http://www.webtexttool.com because the tool is very easy to use and it allows you to keep the overview of all the things you should take into account with regard to SEO.
Top plugins are SEO by Yoast and All In One SEO. I prefer using All In One SEO, because it is as it says All in one. It supports XML sitemap, Twitter cards, Google Analytics, robots.txt. Basicly, it provides everything what is required for quality SEO. SEO by Yoast is the main competiton of All in one SEO plugin they are very simillar but Yoast requires additional plugins for Google analytics, sitemap, etc.
I'd recommend Yoast SEO plugin. I'm using for all my WordPress sites and preferring for my clients' sites as well. Very useful and effective.
Creating a Site Map, integrating Google Analytics, and ensuring that each post is SEO optimized will be sure to improve your SEO rankings. It is also highly recommend to carefully word META Keyword descriptions for each post on your site in order to improve the likelihood of your content being shared. Hope this helped!