Here are some free useful tools that will help in order to achieve top ranking in SERPs and to stay there.

• Google Keyword Tool has recently been replaced by Google Keyword Planner. It helps you to develop the right list of keywords for your website.
• Wordstream another free useful tools, performs better than even some of its paid alternatives with huge database carrying thousands of unique word ideas.
• Ubersuggest helps you to develop long tail phrases
• Removeem is a helpful tool to identify the anchor text diversity on your page, you can use and avoid over optimization
• Copyscape is the well known tool to check plagiarized content on your page, both Removeem and Copyscape have become even more important to use after Google’s Panda.
• Sitemapinspector helps you to get your XML sitemap free from errors in order to achieve better position in search engines
• Woorank lets you generate a free report after analyzing various factors of your website like title description and keyword tags of your website, mobile visibility of your website, keyword consistency, social reach of your website etc. It also suggests the areas of improvement.
• Google Analytics has become one of the integral tools out there to analyze the traffic to your website. It provides a massive amount of information about the behavior of traffic on your website, if you want to expand your business on Internet you have to consider Google Analytics.