Typically on the hood. If the chip is not deep down to the metal, I ignore it. However, I’m seeing some little ones ( about 2 mm dia) where rust shows up. What should be done about those? Car has lots of mechanical life left.
Spot-grind them down to metal and touch them up with primer and paint. A Dremel tool might be perfect for this job.
You shouldn’t let the chips get to the point where they rust. If you are doing a lot of highway or gravel road driving, check at least twice a month or more. Use a bottle of touchup paint in your car’s color and regularly touch up chips as soon as they appear so they won’t rust. Once they have, grind, prime, and paint like @the same mountainbike suggests.
I keep a bottle of brush-applied touchup pain in my small toolbox in back of my car. That allows me to tough up a chip as soon as it happens, before it starts to rust. It’s worked well for me over the years.
Thank you! And now I have an excuse to get a Dremel tool :>)
What year/make/model?
Car two years old? repair it
Car 15 years old? Is it worth it?
It is if you’ve been looking for an excuse to get a dremel tool… 
Yup, when I buy a car, one of the first things I do is get a bottle of touch up paint from the dealer. Better be real careful if you’re trying to grind the rust out though or it’ll be hard to fill in the spot so it looks ok. Depending, you might want to try a chemical rust remover instead. Then a little spot of prime and paint. Dupont used to make an acid type cleaner that was pretty good and would only be available from a auto paint supply store, or maybe one of the others like Navel Jelly or something if you stay at it.
I find small hood chips easier to fill using a wooden toothpick and filling the chip without going over the edge of it. Surface tension will let you build up the paint slightly higher than the hole and when it dries it will be level.