As others have mentioned, it would help to have an idea of what and how you're trying to market.
Do you have an online funnel for a digital product or SAS?
Do you have a brick & mortar location selling a tangible product?
Are your sales confined to a local area, a region of your country, the entire country, or international?
Are you selling products or services?
Is your typical customer giving you $10, $1000, or $100,000 per sale?
Are you trying to create ads? If so, are they ads on social media (Facebook, IG, etc.) in newspapers? in trade publications?
Are you trying to use a content marketing strategy like blogging, free e-books, etc.?
Having said that, I like Donald Miller's "Business Made Simple" as a general overview. The most important strategy in marketing is to talk about your customer's problems and then share how you have a solution to those problems.