Keep it simple.
Open a Google Sheet. Create two columns.
Pretend you're a prospective client. You're looking for a widget, or a pair of shoes, a nice pasta dish, or medical services. What would someone type, who is searching for what YOU offer?
Now pretend you're an existing client, or a client who has heard of your business or perhaps seen an ad or a car wrap.
What would you type?
Review your lists, and fine- tune them.
Sort them by priority- which ones are most important, valuable, and relevant to you?
These are now your keyword targets.