This can be very tedious work and if you don't do it right it has the chance of almost looking worse when you're done.
Basically you want to clean the area with a wax & grease remover and then slightly dilute your touch up paint with some lacquer thinner and use a very fine tipped artists brush to apply the paint to the rock chip. Apply a little at a time and let it dry, repeating this until it builds up above the surrounding area. Some light wet sanding will level it and then you need to compound the area to remove the sanding marks. Do NOT use a rubbing compound by hand because you'll just screw up the surrounding paint.
Doesn't sound like a ton of fun at this point, does it??
You might also want to look into the Langka system (
LANGKA Paint Chip and Scratch Repair) and give that a shot. I've seen it used with decent results, but the best results still included some wet sanding and compounding by machine to remove the sanding marks.
In all honesty though, if you aren't real comfortable with wet sanding and machine compounding (most people only
think they know what they're doing), I'd probably leave it to a pro.