This is a very common issue that non painters and beginers have.
I hope you have fixed your issue but incase not or for those that need more advice....
I have this problem too. But I have been able to counter it and continue painting by:
after your done for the day or event turn over the can and depress the nozzle. Spray out any extra paint left in it. (just get the major bit. dont depress for ever as youll lose all your pressure in the can.)
Sometimes when doing the above you still have those nozzles that get funked up. This is why I keep evey nozzle from ever empty can that I tose out. If the can is spraying good when I empty it... I keep the tip. and swap it out for a tip that is spitting all over my art.
Then of course you need to be sure you are keeping the tip clear of the paint that dries in the out side of it. Before you start a project go through all of your cans and clean off the clumpy coverings that are on them. Scraping them with your finger nail or a pallete knife works great.
Hope this helps someone.