A couple things:
1: Make sure the nozzle is open. It sounds like something stupid to check, but its a mistake that many (myself included) have made.
2: Make sure there is no paint dried in the nozzle itself. If there is, you will need to clean it out. I have found that the Testors/Model Master Metalizer thinner is a great solvent, even for dried acrylics (a real ****** to remove). Just make sure if you use it, that you are careful and don't spill it anywhere you wouldn't want it.
3: When using the can of propellant, you should keep it in a bucket of warm water (not hot, just warm). It works better this way.
4: If you can, get a compressor or air tank (a large one like the type used for helium or even propane). I got a decent compressor for about $120 about 2 years ago and am completely happy with it.
5: Hyperscale is a great place to check out. Another place to check out is
Aircraft Resource Center. There are some good tips and such there. Also, the forums there are a little easier to use as they are very simliar to this one.
Good luck with the model!