Read the faq. its got everything in it. heres a link
FAQ
the bubbles are probably due to the fact that you didnt prime the plastic with primer. the paint didnt stick well to the surface and now you have bubbles. You should also make sure that you have a clean surface to paint as well. the oil from your fingers can ruin a paint job. so clean the part first with some detergent and water. let it dry completely. lay some primer down on it, let it dry comepletely. then you can spray whatever color you want. (you may want to lightly sand between coats and dont forget to wash off the dust)
here's what i would do with the situation you have right now... I'd strip the paint and start over with primer... the hard core modelers on this forum wont let you get away with not priming. read the faq to find out how to strip the paint.
The main point though is to READ THE FAQ. it may take a while but you'll be a better modeler from it.