If you want to try SEO, the first step is an easy one. Before jumping into the SEO experience, it helps if you have an SEO Audit to get an idea of what is needed for your website.
An SEO Audit is not an evaluation of every page of your website unless you request it to be. Normally, the audit will evaluate a few pages of your website which are significant for your business. This means looking at some of your major product or service pages. If those pages show that there is a glaring need for SEO, that suggests that less important pages of your website are also in dire need of optimization.
After an SEO Audit, you can create a plan to implement optimization of your entire website or, at minimal, of those aspects which you especially want to monetize.