There aren't fixed steps or procedures when it comes to painting. There are some basics although they are not fixed rules such as painting on the lightest color first, applying a light colored primer when plastic is dark and finish color is light etc. Common sense applies when it comes to the basics. You've got to take each situation as almost unique, and plan its paint/masking job accordingly. Some pointers are: how will application of a certain color affect subsequent steps, can the finish just applied be masked, if using a mix of solvent based and aqueous paints, you're well advised to plan using aqueous over solvent-based and not other way around. Try to envision the whole job progressing, and you should be able to 'see' the pitfalls and thus plan an effective sequence.
Sorry but don't think there's a straight answer to this one.
Cheers!