Serenity, as a starting guideline, here's what I do.
I first make sure I have profiles of the bird I want to do. Then I do research on the plane in general to understand the different parts on the plane and different types of materials. Then I look for museum pics to see what the rivets and panel lines look like on it. After I've gathered this info, then I'll start making a skin.
I first start out with just making sure I can get the colors as close to being correct as possible. Then I paint the skin 1 color (base color) and I do not just fill the entire file with 1 color, I actually try to only paint in areas that affect the outter skin of the plane, and not things such as engines, props, inner wheel wells and such things like that. Then I make the panel lines. After the panel lines are made I then do the camoflauge and use the panel lines as guidelines to help me get things right. Then I make the rivets. Then I'll do 3d shading, control surfaces. Then I'll do texture for the skin, grime, dirt, paint chips, paint fading and exhaust stains. Then I'll go back and work on the transparencies of the panel lines, rivets and everything else. Then I'll fix color transistions so that they blur better and then even tweak color levels. Then I'll make sure I do engines, wheels, props and letters, codes & noseart. I'm constantly also going back to redo things if they don't look right. Figure 80 hours to make a skin. I use photoshop so whenever I make a change, it only takes me 1/2 a second to see the change in the film viewer. Remember to use AH to see what it will really look like with the better lighting in the game.