Using spray cans

I hold it even closer- about a foot to 15 inches- but keep the can in rapid motion.  Can must be moving before valve depressed, release valve while still moving.

If you are doing a car, I assume you are using gloss paint.  Gloss painting is an exercise in brinksmanship.  You need to get a reasonably wet coat on, stopping just a second before it runs.  How do you know the second before it runs?  Experience with that paint.  So practice any time you go to a new brand of paint.  It is much easier with an airbrush because it is going on slower.

One idea I often use is to put a base coat down with a rattle can, but stop WELL before it runs.  This will be a bit dry and hence not so glossy. I then sand that coat with 1000 grit.  Then airbrush a thin, wet final coat.

I agree, light coats, avoid putting too much paint on the surface at one shot.

I use rattle cans for all large surfaces at this point, like the exterior of an aircraft or armored vehicle, I still haven't worked up to using the airbrush I bought years ago.  But I've been practicing using a light touch, when spraying paint from the can.

I also move the can across the work to be painted.  I'll move from left to right, for example, and start the motion before I press the nozzle, dispense the paint, and release the nozzle as my hand moves past the work.

But above all, light coats, light coats, light coats.  Let it build up.

I guess that's true, too, generally speaking, of spraying with an airbrush, too.  Too much at once, and it'll puddle and run.

Using rattle cans is an art unto itself!

I warm up the can using warm water (not boiling hot!), and shake vigorously and frequently. I also spray no more than 12" from the surface. Start by spraying off the model and end off the model and use light coats. Trying to get full coverage on one pass is inviting runs, as you've discovered. Depending on the color you might want to do three or more passes.

I've added a video (not mine!) showing the basic technique. Note the use of a holder for the body, and the glove. The glove is especially important if you don't like multi-colored hands!

Light misting coats allowing time for them to set before applying the next. Once coverage is reached and cured you can rub out the paint to ease the orange peel effect.

And why were you worried about getting too much inside the car? Was it assembled? Usually one paints the body BEFORE assembly. Just like they do the real deal.