One thing that helps is to use the right masking tape. The common tan-colored stuff that's used for painting houses is almost guaranteed to rip off any paint under it. Tamiya makes a tape that's designed for models. It has a lower tack, and probably (not necessarily) won't pull off the paint under it - provided that coat is nice and dry. I recently bought, from MicroMark, a couple of spools of tape made by 3M. I haven't had occasion to use it much yet, but it's promoted as being easy to peel and it can take curves nicely.
I think some modelers (I'm not talking about GM, or Don, or Bill) haven't figured out what primer does for them. It does NOT stick better to the plastic than the finish coat. Modern hobby paints are specifically formulated to stick to styrene. If they don't (after reasonable drying time), either the modeler has done something wrong or the particular bottle of paint is defective.
The other benefit of primer is that it makes all the parts under the finish coat the same color. Theoretically I guess that shouldn't matter, in that the finishing coats can cover up whatever color is under them. In practice, though, if you try to paint a piece of black plastic bright yellow, it will take several coats to cover the black completely - and by the time that happens the yellow paint may be so thick that it conceals details. And if you've got some light grey filler on the joints in the black plastic, it will take a lot of coats to obliterate the border between the two. That's where a coat of nice, neutral grey primer really helps.
I'm not suggesting that primer is useless. Far from it. But the modeler needs to be aware that the primer accomplishes some things and doesn't accomplish others.
My most recent major paint job was the hull of the plank-on-solid wood fishing schooner I'm working on. After gluing all the basswood planks to the hull, and sanding them smooth (which took forever), I followed the advice of a modeling friend and gave the whole hull exterior two coats of old-fashioned AeroGloss sanding sealer. (My wife thereby got her first exposure to the delightful smell of airplane dope.) I let it dry for a day after the second coat, scuff-sanded it once more, and painted the bottom with Model Shipways acrylic. Then I waited several hours, laid down some Tamiya masking tape at the waterline, and painted the above-the-waterline planking with Model Shipways "hull/spar black." Worked fine.
This is one area where wood is easier to work with than styrene.
Youth, talent, hard work, and enthusiasm are no match for old age and treachery.