Create a digital marketing strategy - how?

Start backwards from the number that pays the bills. How many leads or sales a month do you need, and what is one worth? That tells you what you can afford to spend getting one. Then work out who buys and where they already look - search, one particular social app, word of mouth, email. Pick one or two channels you can do properly rather than six badly. Get tracking in place before spending anything (conversions set up in GA4 at the very least), run it for a quarter, and cut whatever isn't producing. Most strategy documents fail because they list every channel going and never say what success looks like.