I think general familiarity with the software you choose to use is a must. We can offer all manner of tips, suggestions, tricks, etc, but none of it will really replace or fill in for general knowledge of the software.
So play with it! Rather, make things in it! Do some webpage banners to start out, try small projects like re-creating US markings. Play around and try to duplicate your favorite bomber's nose art (this will involve a lot of different tools and will be good practice).
There are also many online tutorials, non-specific to Aces High, that can help you out here.