You know that you are supposed to turn a spray paint can up-side-down to clear the paint out of the nozzle before storing it. That works fine if you use it just a few times, but if you use it frequently for very small paint jobs, some people are worried about running out of gas before you run out of paint.
The suggested trick is to take the nozzle off of the paint can, and spray some kind of lubricant through. This will chase out the paint and leave something that will not dry and block the passage. When you run paint back through, give a quick spray away from your project to clear out the oil.
Of course the paint companies say that there is enough propellent in the can to no have to do this -- and they point out that often the paint cloggs not in the nozzel but in the stem and you will have not cleaned out the stem with this technique.