Make things! When he sees your delight at creating new things and bringing them to life, he will likely mimic you, as is common in younger children.
Teach him skills. Whether you sign him up for a shop class or baking lessons, he’ll learn not only tangible skills (e.g. to use a lathe if it’s a shop class) but also the intangible skills that comprise the maker mentality — estimation (how long should this bake for if my oven always underheats things?), scaling (hmm, what if i want to make 23 cupcakes instead of 11), innovating (i bet this frosting would take yummy with some cinnamon), etc.
Let him spend money. ”Making” has costs. To learn how to sew, you need a needle, thread, some cloth, and if you don’t have any ideas, a template. A lot of parents urge their kids to be resourceful, regardless of the task at hand but this isn’t always most encouraging thing to hear: “Oh you want to build a model rocket with an on-board camera? That sounds cool. You can do it if you buy all the parts yourself.”
Leave him alone. Building, especially at a young age, is a solitary activity. It requires time to think about what you want to build or change and lots of editing, chiseling, re-writing, etc. If your kid’s schedule is jam-packed with all sorts of activities (swim for two hours, then rush to ballet lessons, then eat dinner with family, then homework, then night time art…), he’ll never have the requisite time to do the kind of reflecting that is needed for making things.
Inspire him. Bring home cool stuff (cool for you, not for him) — that sounds vague but my parents always brought home things that they thought were awesome. They would tell me how X was the softest or loudest or sharpest X that existed and why that was important or new or interesting. It wasn’t huge, but it got me thinking…