I’ve actually completed all 6 of the SEO courses on Coursera that @simonebogni mentioned and they’re very good, you get a lot of useful information and there are a bunch of projects to help you get some independent practice. However, SEO is just one part of digital marketing, so you might also want to explore SEM (search engine marketing, which is basically paid advertising on search engines), and even social media as an additional channel of website/product/content promotion.
And one more thing. As @DanCouper hinted, you don’t want ‘as much clientele as possible’. What you want is as many converting clients, meaning that people who land on your site actually do what you want them to do (buy your product, read and share your content, subscribe to your podcast, or whatever else your aim is). Defining your target audience, figuring out what they search for and what they expect to find on your website once they’re there should be your first step.
One more thing that you should be aware of in case you’re not already - domain authority is a huge ranking metric on search engines and it pretty much depends on how many other websites and which ones link to yours (this is extremely hard to manipulate, so don’t even bother trying). The point is - it might be veeeery tough to compete with ‘other giants’ in your target industry, if not impossible. I don’t mean to discourage you, but it’ll take a huge effort!