How would I paint wood slat blinds?

You can use Rustoleum spray paint. I would use a spray primer first then the color of your choice for the second and possibly third coat. You can also buy Rustoleum Chalked paint in a spray can. It is the Rustoleum brand of chalk paint and comes in both a regular can and a spray paint. If you choose to use the Rustoleum Chalked spray paint please buy the clear sealer that comes with this product line. I have tried to use other brands of clear sealers/poly with this Rustoleum Chalked spray paint and have had trouble with bubbling and crackle lines. I do like this line of chalk paint in a spray can. You will have a very smooth matte finish. If you choose to use the Linen White color it does take more than a few coats---so using primer first is still a good option even though you don't have to prime with chalk paint. I have waxed over this paint successfully rather than using the clear sealer but I don't think I would wax blind slats.

I would spray them with this primer. https://amzn.to/2W5q96v

Then, use a latex paint or chalk paint of your choice to paint them. Personally, I would use a semi-gloss latex paint.

I've sprayed blinds in the past. I only needed to paint one, so I used a spray paint. If you are doing a lot of them you probably want to use a sprayer.