Dots , Dagger strokes , Fades and blends. does not make a difference if it is small detail of a 40 foot panel you have to have the basics down pat before you can get the detail you want.
But what I do if you really want to know is start out painting a picture 8X10 than make the same picture 4X6 and than 2X3 same picture same detail. it is easy to make a large painting look like it has a lot of detail but hard to make a small one.
Look up an artist name Marissa Oosterlee http://marissaoosterlee.com/2011/09/23/airbrush-show-2/
on a few other forums I am on she has posted some really small and amazing work. She is also the one who told me to practice doing the same painting smaller and smaller . You gain more control over your airbrush and learn how to play with air pressure and reduction of paint doing it this way.
does not make a difference if it is a skull or a portrait on what you paint but make the largest one with as much detail as you can get. than make the smaller ones look just like it.
It is a hard thing to do when you are first starting.
Also exactly what kind of detail are you talking about ? To me detail is the smallest of items on a painting. IE , ring design on a finger , or small threads off a piece of cloth,
Here you will see a paint of a guy standing on a bridge to the right of his head is a grain of rice. Is this the type of detail you are looking to get..http://marissaoosterlee.files.wordp...ingwithricegrain2-e1315689744293.jpg?w=700&h=