Exactly what Forbes/hutton mentioned, and if you have a single shot or double with extractors well then! Thats the only way it gets easier!
If your asking about pumps? well I find people pick up on a side eject faster oppose to a bottom eject such as a Ithaca. (I sure do love my Ithaca though!)
Semi autos are pretty simple aswell again some people have troubles with the shell latch, while loading them. After you have inserted your ammo, you pull back the action.
I also find people who I take out who are new, always want to insert the cartridge in a chamber first instead of the tubular magazine, I always sit their and explain to them once I can tell they are super comfortable with loading and un loading, and are responsible enough with their muzzle direction, and fingers always off the trigger. Then I will show them how to load tactically or directly in to the chamber. No way am I going to let a first time shooter sit their and load directly in to the chamber.