On Page SEO Checklists

Hey guys, I've secured a job as a digital marketing analyst. So as a training project I must do on Page SEO on a website that provides SaaS.I have to find the reason why it's ranking on one of its primary keyword is low and the ways to rectify them. So how should I go on with this.

Apart from keyword research, competitor analysis and content analysis what are the major points I should check. Regards✌️