Pinstriping is a skill. The more you do, the better you get. That said...

I did some pin stripping on my first Legnano Gran Premio. The fenders were done with a paint pen, freehand, and they turned out pretty good...



The black stripes on the seat tube are plastic stick on tape, available at most automotive stores...



The same goes for the red stripes on the stays and fork blades...



And keep in mind, the striping does not have to be perfect. It rarely was, in Old School days.