Start making kits, and pay attention to lengths, diameters, etc. of the components, etc.
Make a closed-end pen, off of a Baron or El Grande kit.
Mandrels for that from ArizonaSilhouette.
Pay attention to those lengths, but also proportions and visual elements.
Look at "kitless" pens - from folks here, at fountainpennetwork.com, and from the manufacturers. Are they doing closed ends, sections, metal pieces where? why?
Read a LOT - taps, dies, what goes with what? what can you decide vs. what you have to meet/match? Read that tap/die chart I posted to Adv.Pen-Turning subforum
Jump in - buy some taps/dies (start cheap with single threaded ones).
Practice threading on cheap $1/ft acrylic and acetyl.
Read a LOT more - now you know some certain issues/focuses you should read about vs. general info. The various postings will make better sense now you see some of the challenges.
Go for it. and loop/repeat the last few points over and over (read, search, contribute, try)
-- joe