You can de-index any types of content that have less than 100 words. This might be the #1 suggestion for most businesses that have not done any SEO. For WordPress websites you can use the Yoast SEO plugin for this.
2. You can find terms that are driving traffic to your competitors with a tool like Ahrefs, or SEMRush and create similar but more in-depth and quality content for the same terms. Consider the intent of the searcher and create epic content that will service that intent while at the same time selling them your products or services with a lead generation form or listing of products.
3. You can reach out to higher trafficked websites that people in your prime demographic are reading, and ask if you can write a blog post for them. Create a quality piece of valuable content and use your bio at the bottom of the post to create a compelling picture of the products or services you offer and link to your website. Earning links from high domain authority sites (determine this with a tool like Mozbar) is the #1 thing you can do to drive visibility of your site up.