if its urethane... wash it really well with soap and water first. using a grey or white scotch brite pad.

dont be scared to wash it a few times. once its dried really well get the appropriate plastics adhesion promoter.. SEM makes some really good plastic paint and prep materials we use it a good bit at my shop. they dont sell it at the parts stores but any automotive body and paint supply shop will carry it. apply the adhesion promotor as instructed on the label ( directions vary depending on what type of plastic you have so read the label). no high build primer is needed. what most people are forgetting is that plastic and urethane stuff is flexible, some more so than other and rattle cans dont have flex agents in them... definitly not high build primer **** will crack and flake off). if you have got any deep scratches in it then wet sand them out first before you apply anything, then wash well, ahesion promo and so on.. ). after the ahesion promoter is applied go to the color stage. rattle can dries really thin so it will take a few good coats 3-5 for full coverage. use a can that has a fan tip not the round type ( on most fan tip cans the nozzle is blue). like someone else wrote in the duplicolor stuff is really good for spray can. the first coat should be light and even dont try to make it slick and fully colored on the first coat, depending on the temperature wait 5-10 mins and come back with another coat this time a little heavier than before, overlapping slightly to eliminate any stripping from happening, wait another 5 or so and come over it again. after 3 coats if you dont have any holidays or stripes you should be good to wait and put down some clear. if you dont have any problems in the black let it dry the recommended time then move onto clear. apply the clear in the same way. light first coat, then medium wet coats after that. the last coat you put on you want to be wet and smooth dont run it but make sure its pretty shinny. dont worry if the entire thing is not totally glossy as your spraying you will see some orange peel but shortly after you spray the last coat as its curring it will float out and lay down slick and leave you with a decent spray bomb job. good luck. i paint high end muscle cars and collector cars for a living so if you need any help let me know. my shops is near buford hwy off pleasant dale. pm me if needed. hope some of this was helpful