When it come to backlink research and audit, there is no better tool then AHREFS. You can use AHREFS to uncover your competitors' backlink profile and build your own backlinks.
YOASTSEO is an all-in-one SEO tool for Wordpress which make handling of all the basic aspects of On-Page SEO look simple.
GTMetrix is an excellent tool to test the performance of your website. It is a free tool which evaluates your site speed and provides useful tips to speedup your website.