Kristen, in each addition to the 3 dozen help articles on SEO that are referenced in the SEO Deep Diver article that Michelle shared, here are some more resources:
(1) SEO cheat sheet: https://www.marketo.com/cheat-sheets/seo-cheat-sheet-best-practices-for-on-page-optimization/
(2) Short video giving an overview of SEO (not product-specific info): from the Community, click on University, then click on Videos, and then you'll see an SEO video
Michelle and Neil: we do offer paid SKUs that allow more keywords, search engines and/or sites. I've asked your respective Customer Account Managers to reach out to you. Thanks!